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Bacteria and viruses are a natural component of Earth biodiversity and play an essential role in biochemical and geological cycles. They may also pose problems outside their native range, where they can negatively impact on natural resources, wildlife, and human health. To address these challenges and develop sustainable conservation strategies, a thorough understanding of their invasion related- factors is needed: origin, country and year of introduction, and pathways dynamics. Yet, alien bacteria and viruses are underrepresented in invasion ecology studies, which limits our ability to quantify their impacts and address future introductions. This study provides primary datasets of alien bacteria and viruses of plants and animals present in the European environment. The datasets contain expert-revised data on 446 taxa and their invasion related- factors across terrestrial and aquatic environments. Taxa information are complemented with spatial occurrences. The datasets provide a basis for collaborative initiatives to improve the collection of alien bacteria and viruses’ data, and a starting point for data-driven conservation practices.

Mechanical forces and tissue mechanics influence the morphology of the developing brain, but the underlying molecular mechanisms have been elusive. Here, we examine the role of mechanotransduction in brain development by focusing on Piezo1, a mechanically activated ion channel. We find that Piezo1 deletion results in a thinner neuroepithelial layer, disrupts pseudostratification, and reduces neurogenesis in E10.5 mouse embryos. Proliferation and differentiation of Piezo1 knockout (KO) mouse neural stem cells (NSCs) isolated from E10.5 embryos are reduced in vitro compared to littermate WT NSCs. Transcriptome analysis of E10.5 Piezo1 KO brains reveals downregulation of the cholesterol biosynthesis superpathway, in which 16 genes, including Hmgcr, the gene encoding the rate-limiting enzyme of the cholesterol biosynthesis pathway, are downregulated by 1.5-fold or more. Consistent with this finding, membrane lipid composition is altered, and the cholesterol levels are reduced in Piezo1 KO NSCs. Cholesterol supplementation of Piezo1 KO NSCs partially rescues the phenotype in vitro. These findings demonstrate a role for Piezo1 in the neurodevelopmental process that modulates the quantity, quality, and organization of cells by influencing cellular cholesterol metabolism. Our study establishes a direct link in NSCs between PIEZO1, intracellular cholesterol levels, and neural development.

A new species of the genus Agoo Bahder & Bartlett, Agoo beani sp. n. was found associated with coconut (Cocos nucifera L., Arecaceae) in Jamaica. This species was discovered as part of a survey of the Caribbean basin to document planthopper diversity on palms. Cytochrome c oxidase subunit I (COI) and 18S sequence data strongly support placement of the new species in Agoo. The morphological features of Omolicna cocoana Rodriguez-Leon & Hidalgo-Gato from Cuba are reviewed and this species transferred into the genus Agoo.

Tethered photoswitches are molecules with two photo-dependent isomeric forms, each with different actions on their biological targets. They include reactive chemical groups capable of covalently binding to their target. Our aim was to develop a β-subunit-tethered propofol photoswitch (MAP20), as a tool to better study the mechanism of anesthesia through the GABA(A) α1β3γ2 receptor. We used short spacers between the tether (methanethiosulfonate), the photosensitive moiety (azobenzene), and the ligand (propofol), to allow a precise tethering adjacent to the putative propofol binding site at the β(+)α(−) interface of the receptor transmembrane helices (TMs). First, we used molecular modeling to identify possible tethering sites in β3TM3 and α1TM1, and then introduced cysteines in the candidate positions. Two mutant subunits [β3(M283C) and α1(V227C)] showed photomodulation of GABA responses after incubation with MAP20 and illumination with lights at specific wavelengths. The α1β3(M283C)γ2 receptor showed the greatest photomodulation, which decreased as GABA concentration increased. The location of the mutations that produced photomodulation confirmed that the propofol binding site is located in the β(+)α(−) interface close to the extracellular side of the transmembrane helices. Tethering the photoswitch to cysteines introduced in the positions homologous to β3M283 in two other subunits (α1W288 and γ2L298) also produced photomodulation, which was not entirely reversible, probably reflecting the different nature of each interface. The results are in agreement with a binding site in the β(+)α(−) interface for the anesthetic propofol.

A new species of cixiid planthopper (Hemiptera: Fulgoroidea) in the genus Oecleus Stål, Oecleus mackaspringi sp. n., is described from Spring Garden, Jamaica. This new taxon is associated with coconut palm (Cocos nucifera L.) and was found while surveying palm plots with active cases of lethal yellowing (LY). This is the first report of the genus Oecleus from Jamaica. Sequence data for the COI gene and 18S gene are also provided.

The mycotoxin zearalenone (ZEN), which frequently contaminates cereal-based human food and animal feed, is known to have an estrogenic effect. The biological response associated with exposure to ZEN has rarely been reported in organs other than the reproductive system. In the intestine, several studies suggested that ZEN might stimulate molecular changes related to the activation of early carcinogenesis, but the molecular mechanisms behind these events are not yet known. In this study, we investigated gene expression and changes in protein abundance induced by acute exposure to ZEN in the jejunum of castrated male pigs using an explant model. Our results indicate that ZEN induces the accumulation of ER but not ER, modulates Wnt/&beta, catenin and TGF- signaling pathways, and induces molecular changes linked with energy sensing and the antimicrobial activity without inducing inflammation. Our results confirm that the intestine is a target for ZEN, inducing changes that promote cellular proliferation and could contribute to the onset of intestinal pathologies.

Propofol (PFL, 1-hydroxyl-2,6-diisopropylbenzene) is currently used widely as one of the most well-known intravenous anesthetics to relieve surgical suffering, but its mechanism of action is not yet clear. Previous experimental studies have demonstrated that the hydroxyl group of PFL plays a dominant role in the molecular recognition of PFL with receptors that lead to hypnosis. To further explore the mechanism of anesthesia induced by PFL in the present work, the exact binding features and interaction details of PFL with three important proteins, human serum albumin (HSA), the pH-gated ion channel from Gloeobacter violaceus (GLIC), and horse spleen apoferritin (HSAF), were investigated systematically by using a rigorous three-layer ONIOM (M06-2X/6-31+G*:PM6:AMBER) method. Additionally, to further characterize the possible importance of such hydroxyl interactions, a similar set of calculations was carried out on the anesthetically inactive fropofol (FFL, 1-fluoro-2,6-diisopropylbenzene) in which the fluorine was substituted for the hydroxyl. According to the ONIOM calculations, atoms in molecules (AIM) analyses, and electrostatic potential (ESP) analyses, the significance of hydrogen bond, halogen bond, and hydrophobic interactions in promoting proper molecular recognition was revealed. The binding interaction energies of PFL with different proteins were generally larger than FFL and are a significant determinant of their differential anesthetic efficacies. Interestingly, although the hydrogen-bonding effect of the hydroxyl moiety was prominent in propofol, the substitution of the 1-hydroxyl by a fluorine atom did not prevent FFL from binding to the protein via a halogen-bonding interaction. It therefore became clear that multiple specific interactions rather than just hydrogen or halogen bonds must be taken into account to explain the different anesthesia endpoints caused by PFL and FFL. The contributions of key residues in ligand-receptor binding were also quantified, and the calculated results agreed with many available experimental observations. This work will provide complementary insights into the molecular mechanisms of anesthetic action for PFL from a robust theoretical point of view. This will not only assist in interpreting experimental observations but will also help to develop working hypotheses for further experiments and future drug design.

Intravenous anesthetic agents are associated with cardiovascular instability and poorly tolerated in patients with cardiovascular disease, trauma, or acute systemic illness. We hypothesized that a new class of intravenous (IV) anesthetic molecules that is highly selective for the slow type of γ-aminobutyric acid type A receptor (GABA(A)R) could have potent anesthetic efficacy with limited cardiovascular effects. Through in silico screening using our GABA(A)R model, we identified a class of lead compounds that are N-arylpyrrole derivatives. Electrophysiological analyses using both an in vitro expression system and intact rodent hippocampal brain slice recordings demonstrate a GABA(A)R-mediated mechanism. In vivo experiments also demonstrate overt anesthetic activity in both tadpoles and rats with a potency slightly greater than that of propofol. Unlike the clinically approved GABAergic anesthetic etomidate, the chemical structure of our N-arylpyrrole derivative is devoid of the chemical moieties producing adrenal suppression. Our class of compounds also shows minimal to no suppression of blood pressure, in marked contrast to the hemodynamic effects of propofol. These compounds are derived from chemical structures not previously associated with anesthesia and demonstrate that selective targeting of GABA(A)R-slow subtypes may eliminate the hemodynamic side effects associated with conventional IV anesthetics.

During 2010-14 surveys in the major sesame growing areas of Fars, Yazd and Isfahan provinces (Iran), genetic diversity and vector transmission of phytoplasmas associated with sesame phyllody were studied. Virtual RFLP, phylogenetic, and DNA homology analyses of partial 16S ribosomal sequences of phytoplasma strains associated with symptomatic plants revealed the presence of phytoplasmas referable to three ribosomal subgroups, 16SrII-D, 16SrVI-A, and 16SrIX-C. The same analyses using 16S rDNA sequences from sesame phyllody-associated phytoplasmas retrieved from GenBank database showed the presence of phytoplasmas clustering with strains in the same subgroups in other Iranian provinces including Bushehr and Khorasan Razavi. Circulifer haematoceps and Orosius albicinctus, known vectors of the disease in Iran, were tested for transmission of the strains identified in this study. C. haematoceps transmitted 16SrII-D, 16SrVI-A, and 16SrIX-C phytoplasmas, while O. albicinctus only transmitted 16SrII-D strains. Based on the results of the present study and considering the reported presence of phytoplasmas belonging to the same ribosomal subgroups in other crops, sesame fields probably play an important role in the epidemiology of other diseases associated with these phytoplasmas in Iran.

Alcohols inhibit γ-aminobutyric acid type A ρ1 receptor function. After introducing mutations in several positions of the second transmembrane helix in ρ1, we studied the effects of ethanol and hexanol on GABA responses using two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes. The 6' mutations produced the following effects on ethanol and hexanol responses: small increase or no change (T6'M), increased inhibition (T6'V), and small potentiation (T6'Y and T6'F). The 5' mutations produced mainly increases in hexanol inhibition. Other mutations produced small (3' and 9') or no changes (2' and L277 in the first transmembrane domain) in alcohol effects. These results suggest an inhibitory alcohol binding site near the 6' position. Homology models of ρ1 receptors based on the X-ray structure of GluCl showed that the 2', 5', 6', and 9' residues were easily accessible from the ion pore, with 5' and 6' residues from neighboring subunits facing each other; L3' and L277 also faced the neighboring subunit. We tested ethanol through octanol on single and double mutated ρ1 receptors [ρ1(I15'S), ρ1(T6'Y), and ρ1(T6'Y,I15'S)] to further characterize the inhibitory alcohol pocket in the wild-type ρ1 receptor. The pocket can only bind relatively short-chain alcohols and is eliminated by introducing Y in the 6' position. Replacing the bulky 15' residue with a smaller side chain introduced a potentiating binding site, more sensitive to long-chain than to short-chain alcohols. In conclusion, the net alcohol effect on the ρ1 receptor is determined by the sum of its actions on inhibitory and potentiating sites.

Anesthetics are thought to mediate a portion of their activity via binding to and modulation of potassium channels. In particular, tandem pore potassium channels (K2P) are transmembrane ion channels whose current is modulated by the presence of general anesthetics and whose genetic absence has been shown to confer a level of anesthetic resistance. While the exact molecular structure of all K2P forms remains unknown, significant progress has been made toward understanding their structure and interactions with anesthetics via the methods of molecular modeling, coupled with the recently released higher resolution structures of homologous potassium channels to act as templates. Such models reveal the convergence of amino acid regions that are known to modulate anesthetic activity onto a common three- dimensional cavity that forms a putative anesthetic binding site. The model successfully predicts additional important residues that are also involved in the putative binding site as validated by the results of suggested experimental mutations. Such a model can now be used to further predict other amino acid residues that may be intimately involved in the target-based structure-activity relationships that are necessary for anesthetic binding.

The molecular mechanism(s) of action of anesthetic, and especially, intoxicating doses of alcohol (ethanol [EtOH]) have been of interest even before the advent of the Research Society on Alcoholism. Recent physiological, genetic, and biochemical studies have pin-pointed molecular targets for anesthetics and EtOH in the brain as ligand-gated ion channel (LGIC) membrane proteins, especially the pentameric (5 subunit) Cys-loop superfamily of neurotransmitter receptors including nicotinic acetylcholine (nAChRs), GABA(A) (GABA(A)Rs), and glycine receptors (GlyRs). The ability to demonstrate molecular and structural elements of these proteins critical for the behavioral effects of these drugs on animals and humans provides convincing evidence for their role in the drugs' actions. Amino acid residues necessary for pharmacologically relevant allosteric modulation of LGIC function by anesthetics and EtOH have been identified in these channel proteins. Site-directed mutagenesis revealed potential allosteric modulatory sites in both the trans-membrane domain (TMD) and extracellular domain (ECD). Potential sites of action and binding have been deduced from homology modeling of other LGICs with structures known from crystallography and cryo-electron microscopy studies. Direct information about ligand binding in the TMD has been obtained by photoaffinity labeling, especially in GABA(A)Rs. Recent structural information from crystallized procaryotic (ELIC and GLIC) and eukaryotic (GluCl) LGICs allows refinement of the structural models including evaluation of possible sites of EtOH action.

The low density lipoprotein receptor-related protein 1 (LRP1) is a ubiquitously expressed cell surface receptor that protects from intracellular cholesterol accumulation. However, the underlying mechanisms are unknown. Here we show that the extracellular (alpha) chain of LRP1 mediates TGFbeta-induced enhancement of Wnt5a, which limits intracellular cholesterol accumulation by inhibiting cholesterol biosynthesis and by promoting cholesterol export. Moreover, we demonstrate that the cytoplasmic (beta) chain of LRP1 suffices to limit cholesterol accumulation in LRP1(-/-) cells. Through binding of Erk2 to the second of its carboxyl-terminal NPXY motifs, LRP1 beta-chain positively regulates the expression of ATP binding cassette transporter A1 (ABCA1) and of neutral cholesterol ester hydrolase (NCEH1). These results highlight the unexpected functions of LRP1 and the canonical Wnt5a pathway and new therapeutic potential in cholesterol-associated disorders including cardiovascular diseases.

Proper regulation of neurotransmission requires that ligand-activated ion channels remain closed until agonist binds. How channels then open remains poorly understood. Glycine receptor (GlyR) gating is initiated by agonist binding at interfaces between adjacent subunits in the extracellular domain. Aspartate-97, located at the α1 GlyR interface, is a conserved residue in the cys-loop receptor superfamily. The mutation of D97 to arginine (D97R) causes spontaneous channel opening, with open and closed dwell times similar to those of maximally activated WT GlyR. Using a model of the N -terminal domain of the α1 GlyR, we hypothesized that an arginine-119 residue was forming intersubunit electrostatic bonds with D97. The D97R/R119E charge reversal restored this interaction, stabilizing channels in their closed states. Cysteine substitution shows that this link occurs between adjacent subunits. This intersubunit electrostatic interaction among GlyR subunits thus contributes to the stabilization of the closed channel state, and its disruption represents a critical step in GlyR activation.

SUMMARY This review examines the evidence for the existence in the gastrointestinal tract of a new subtype (H3) of histamine receptors, previously described in the central nervous system. Study of these receptors is facilitated by the availability of the highly selective agonist (R)α-methylhistamine and the selective antagonist, thioperamide. H3-receptors seem to exert negative control on gastric acid secretion evoked by indirect cholinergic stimuli: their localization is unclear but it seems to be outside the parietal cell. H3-receptors also seem to be located on cholinergic and non-adrenergic non-cholinergic (NANC) neurones of the myenteric plexus, where they negatively control the release of neurotransmitters.

SUMMARY Background: The mechanisms responsible for the gastric ulcerogenic effect of indomethacin are unclear. The importance of basal acid secretion on morphological changes by indomethacin was investigated. Methods: Gastric lesions were macroscopically evaluated 6 h after indomethacin, 20 mg/kg intragastrically, in rats pre-treated with omeprazole (10–100 μmol/kg intragastrically) or lansoprazole (3–30 μmol/kg intragastrically). Glandular mucosa was processed for light, scanning and transmission electron microscopy 3 and 6 h after indomethacin in rats pre-treated with omeprazole (100 μmol/kg) or lansoprazole (30 μmol/kg). Results: After 3 h, indomethacin caused extensive vasocongestion, oedema in the subepithelial region and superficial erosions. After 6 h, deeply extending focal necrosis involved 11 % of the tissue. Leukocyte margination was occasionally seen at 3 h and consistently present at 6 h. Only at 6 h were endothelial cells altered. In rats pre-treated with omeprazole (100 μmol/kg) or lansoprazole (30 μmol/kg) grossly visible lesions were prevented. Oedema, erosions and necrosis were absent. Vasocongestion, vascular leakage and leukocytic margination were seen both at 3 and 6 h while no major damage of endothelial cells was observed. Conclusion: Indomethacin appears primarily to alter microcirculation, and microcirculation damage is dependent on acid for the progression to haemorrhagic lesions.

The mechanisms of general anesthesia in the central nervous system are finally yielding to molecular examination. As a result of research during the past several decades, a group of ligand-gated ion channels have emerged as plausible targets for general anesthetics. Molecular biology techniques have greatly accelerated attempts to classify ligand-gated ion channel sensitivity to general anesthetics, and have identified the sites of receptor subunits critical for anesthetic modulation using chimeric and mutated receptors. The experimental data have facilitated the construction of tenable molecular models for anesthetic binding sites, which in turn allows structural predictions to be tested. In vivo significance of a putative anesthetic target can now be examined by targeted gene manipulations in mice. In this review, we summarize from a molecular perspective recent advances in our understanding of mechanisms of action of general anesthetics on ligand-gated ion channels.

The effect of the selective histamine H3 receptor agonists (R)alpha-methylhistamine, (R)MHA and immepip (IMM) on intestinal smooth muscle contractility was investigated on isolated cells from the longitudinal muscle of the guinea pig ileum. (R)MHA (10(-13)-10(-8) M) and IMM (10(-13)-10(-8) M) did not significantly modify the basal length of intestinal cells; in contrast both agonists (10(-15)-10(-11) M) prevented the contraction produced by acetylcholine (10(-7) M). The (S)-isomer of alpha-methylhistamine, (S)MHA, was inactive both on basal contractility and on acetylcholine-induced contractions. The relaxant effect of (R)MHA was not modified by famotidine (10(-7) M), but totally prevented by the selective H3 receptor antagonist clobenpropit (10(-8) M), which per se did not modify either basal contractility or the contractile response to acetylcholine. These data indicate that inhibitory histamine H3 receptors are present on smooth muscle cells of the guinea pig ileum and can be activated by very low concentrations of selective agonists. It is not clear, however, whether they can have a functional importance in the regulation of intestinal contractility in an intact system.

The compound fedotozine, recently described as a peripheral kappa opioid receptor agonist, was tested on smooth muscle cells isolated from the longitudinal muscle layer of the guinea pig ileum, in comparison with the selective kappa receptor agonist, compound U-50488. Fedotozine (1 nmol/l–1 µmol/l) caused a concentration-dependent contraction of intestinal cells, with a maximum decrease in cell length not significantly different from that caused by acetylcholine. The kappa agonist U-50488 (0.1 pmol/l–100 nmol/l) was without effect. The contractile effect of fedotozine was not significantly modified by naloxone (0.1–1 µmol/l). These results indicate that fedotozine can have direct excitatory effects on intestinal smooth muscle cells from the guinea pig ileum not mediated by activation of kappa opioid receptors.

The trivial name ‘phytoplasma’ has been adopted to collectively name wall-less, non-helical prokaryotes that colonize plant phloem and insects, which were formerly known as mycoplasma-like organisms. Although phytoplasmas have not yet been cultivated in vitro, phylogenetic analyses based on various conserved genes have shown that they represent a distinct, monophyletic clade within the class Mollicutes. It is proposed here to accommodate phytoplasmas within the novel genus ‘Candidatus (Ca.) Phytoplasma’. Given the diversity within ‘Ca. Phytoplasma’, several subtaxa are needed to accommodate organisms that share Ca. Phytoplasma’, a taxon that includes the species ‘Ca. Phytoplasma aurantifolia’ (the prokaryote associated with witches'-broom disease of small-fruited acid lime), ‘Ca. Phytoplasma australiense’ (associated with Australian grapevine yellows), ‘Ca. Phytoplasma fraxini’ (associated with ash yellows), ‘Ca. Phytoplasma japonicum’ (associated with Japanese hydrangea phyllody), ‘Ca. Phytoplasma brasiliense’ (associated with hibiscus witches'-broom in Brazil), ‘Ca. Phytoplasma castaneae’ (associated with chestnut witches'-broom in Korea), ‘Ca. Phytoplasma asteris' (associated with aster yellows), ‘Ca. Phytoplasma mali’ (associated with apple proliferation), ‘Ca. Phytoplasma phoenicium’ (associated with almond lethal disease), ‘Ca. Phytoplasma trifolii’ (associated with clover proliferation), ‘Ca. Phytoplasma cynodontis' (associated with Bermuda grass white leaf), ‘Ca. Phytoplasma ziziphi’ (associated with jujube witches'-broom), ‘Ca. Phytoplasma oryzae’ (associated with rice yellow dwarf) and six species-level taxa for which the Candidatus species designation has not yet been formally proposed (for the phytoplasmas associated with X-disease of peach, grapevine flavescence dorée, Central American coconut lethal yellows, Tanzanian lethal decline of coconut, Nigerian lethal decline of coconut and loofah witches'-broom, respectively). Additional species are needed to accommodate organisms that, despite their 16S rRNA gene sequence being >97·5 % similar to those of other ‘Ca. Phytoplasma’ species, are characterized by distinctive biological, phytopathological and genetic properties. These include ‘Ca. Phytoplasma pyri’ (associated with pear decline), ‘Ca. Phytoplasma prunorum’ (associated with European stone fruit yellows), ‘Ca. Phytoplasma spartii’ (associated with spartium witches'-broom), ‘Ca. Phytoplasma rhamni’ (associated with buckthorn witches'-broom), ‘Ca. Phytoplasma allocasuarinae’ (associated with allocasuarina yellows), ‘Ca. Phytoplasma ulmi’ (associated with elm yellows) and an additional taxon for the stolbur phytoplasma. Conversely, some organisms, despite their 16S rRNA gene sequence being Ca. Phytoplasma’ species, are not presently described as Candidatus species, due to their poor overall characterization.

The influence of pretreatment with (R)-alpha-methylhistamine, selective agonist of histamine H3 receptors, has been investigated on gastric mucosal lesions at different time intervals, from 5 to 60 minutes, after administration of absolute ethanol in the rat. The amount and depth of lesions were quantitatively evaluated by light microscopy. In rats pretreated with (R)-alpha-methylhistamine, the integrity of the mucosa was preserved in approximately 80% of the total mucosal length measured despite ethanol challenge. Prevention of lesion formation was as great at 5 min after ethanol administration as at 60 min. When present, damage involved mainly superficial mucosa and lesions extending deeply into the gland region were evident in 1-2.5% of the total mucosa. Present findings indicate that mechanisms by which (R)-alpha-methylhistamine operates enable the mucosa to counteract damage just from the moment of exposure to ethanol and that protection is exerted both on surface and pit cells and on gastric glands.

The effects of histamine and dimaprit on intestinal smooth muscle contractility were investigated on isolated cells from longitudinal muscle of the guinea pig ileum. Both histamine (10(-14)-10(-10) M) and dimaprit (10(-13)-10(-10) M) exerted a concentration-dependent contraction of intestinal cells, causing a maximum decrease in cell length of about 20%. This effect was not significantly different from that induced by cholecystokinin-octapeptide (CCK-8) 10(-9) M. The concentration-response curves to histamine and dimaprit were shifted to the left in the presence of the histamine H2-receptor antagonist famotidine (10(-7) M) indicating the occurrence in the smooth muscle of H2 receptors mediating relaxation. Whereas the contraction produced by histamine was competitively antagonized by the H1 receptor antagonist mepyramine (10(-8) M), neither mepyramine (10(-7) M) nor temelastine (10(-7) M) did modify the contractile effect of dimaprit. In contrast, atropine (10(-8) M) significantly depressed the maximum response to dimaprit without affecting that exerted by histamine. These data indicate that histamine and dimaprit can modify intestinal contractility, by acting via different mechanisms; while the contractile action of histamine is related to H1 receptor activation, that produced by dimaprit involves cholinergic pathways.

Background: Anesthetics mediate portions of their activity via modulation of the γ-aminobutyric acid receptor (GABAaR). Although its molecular structure remains unknown, significant progress has been made toward understanding its interactions with anesthetics via molecular modeling. Methods: The structure of the torpedo acetylcholine receptor (nAChRα), the structures of the α4 and β2 subunits of the human nAChR, the structures of the eukaryotic glutamate-gated chloride channel (GluCl), and the prokaryotic pH-sensing channels, from Gloeobacter violaceus and Erwinia chrysanthemi, were aligned with the SAlign and 3DMA algorithms. A multiple sequence alignment from these structures and those of the GABAaR was performed with ClustalW. The Modeler and Rosetta algorithms independently created three-dimensional constructs of the GABAaR from the GluCl template. The CDocker algorithm docked a congeneric series of propofol derivatives into the binding pocket and scored calculated binding affinities for correlation with known GABAaR potentiation EC50s. Results: Multiple structure alignments of templates revealed a clear consensus of residue locations relevant to anesthetic effects except for torpedo nAChR. Within the GABAaR models generated from GluCl, the residues notable for modulating anesthetic action within transmembrane segments 1, 2, and 3 converged on the intersubunit interface between α and β subunits. Docking scores of a propofol derivative series into this binding site showed strong linear correlation with GABAaR potentiation EC50. Conclusion: Consensus structural alignment based on homologous templates revealed an intersubunit anesthetic binding cavity within the transmembrane domain of the GABAaR, which showed a correlation of ligand docking scores with experimentally measured GABAaR potentiation.

Improving our understanding of the mechanisms and effects of anesthetics is a critically important part of neuroscience. The currently dominant theory is that anesthetics and similar molecules act by binding to Cys-loop receptors in the postsynaptic terminal of nerve cells and potentiate or inhibit their function. Although structures for some of the most important mammalian channels have still not been determined, a number of important results have been derived from work on homologous cationic channels in bacteria. However, partly due to the lack of a nervous system in bacteria, there are a number of questions about how these results relate to higher organisms. The recent determination of a structure of the eukaryotic chloride channel, GluCl, is an important step toward accurate modeling of mammalian channels, because it is more similar in function to human Cys-loop receptors such as GABAAR or GlyR. One potential issue with using GluCl to model other receptors is the presence of the large ligand ivermectin (IVM) positioned between all five subunits. Here, we have performed a series of microsecond molecular simulations to study how the dynamics and structure of GluCl change in the presence versus absence of IVM. When the ligand is removed, subunits move at least 2 Å closer to each other compared to simulations with IVM bound. In addition, the pore radius shrinks to 1.2 Å, all of which appears to support a model where IVM binding between subunits stabilizes an open state, and that the relaxed nonIVM conformations might be suitable for modeling other channels. Interestingly, the presence of IVM also has an effect on the structure of the important loop C located at the neurotransmitter-binding pocket, which might help shed light on its partial agonist behavior.

The distribution and functions of histamine H3 receptors in the gastrointestinal tract is reviewed with particular reference to the effects on gastric acid secretion, mucosal protection, and intestinal motility. Histamine H3 receptor activation has negative effects on acid secretion induced by indirect secretagogues in cats, dogs, and rabbits; less clear effects were found in rats. An inhibitory effect on histamine release induced by different stimuli was observed in rats, rabbits, and dogs after H3 receptor agonists, thus supporting the idea that H3 receptors occur in ECL cells. (R)-alpha-methylhistamine has a marked protective effect against gastric lesions induced by ethanol in rats, being slightly less effective against aspirin and stress. H3 receptor activation decreases the intestinal motility induced by electrical stimulation in a variety of gut preparations, reducing both cholinergic and NANC neurotransmitter release. In this tissue the inhibitory effects mediated by histamine H3 receptors seem to be coupled, via a G protein, to a restriction of Ca2+ access into the nerve terminal; other mechanisms, however, have been suggested in the gastric mucosa. Histamine H3 receptors have already been subdivided into two receptor subtypes, H3A and H3B, the former being the subtype predominant in the gastrointestinal tissue. The increasing availability of selective agonists and antagonists of H3 receptors will unravel possible novel actions and physiological roles of histamine.

Purpose of review Although general anesthetics have been provided effectively for many years, their exact molecular underpinnings remain relatively unknown. In this article, we discuss the recent findings associated with resistance to anesthetic effects as a way of shedding light on these mechanisms. Recent findings The original theories of anesthetic action based upon their effects on cellular membranes have given way to specific theories concerning direct effects on ion channel proteins. These molecular targets are intimately involved in the conduct of neuronal signaling within the central nervous system and are thought to be essential in the modulation of conscious states. It is the lack of a thorough understanding of unperturbed consciousness that fosters great difficulty in understanding how anesthetics alter this conscious state. However, one very fruitful line of analysis in the quest for such answers lies in the examination of both in-vitro and in-vivo ion channel systems that seem to maintain variable levels of resistance to anesthetics. Summary Information about the possible targets and molecular nature of anesthetic action is being derived from studies of anesthetic resistance in γ aminobutyric acid receptors, tandem pore potassium channels, and an apparently wide variety of protein systems within the nematode, Caenorhabditis elegans.

The accompanying articles in this issue of the journal’s special collection describe attempts to improve on the dynamics of distribution and reduce side effects of analogs of etomidate and benzodiazepines. Both classes of drugs have their principal sites of action on gamma-aminobutyric acid type A receptors, although at very different binding sites and by different mechanisms of action. Herein, we review the structure of gamma-aminobutyric acid type A receptors and describe the location of the 2 likely binding sites. In addition, we describe how these drugs can interact with the nervous system at a systems level. We leave it to other reviewers to discuss whether these new drugs offer true clinical improvements.

The modulatory activity mediated by histamine receptors on the sympathetic nerve transmission was investigated in the rat vas deferens. Agonists and antagonists acting at the different histamine receptor subtypes (H1, H2 and H3) were tested on electrically-driven preparations in vitro. Low-frequency stimulation (0.1 Hz) evoked muscle contractions almost completely-sustained by ATP release, while at high-frequency stimulation (5-10 Hz) norepinephrine was mainly involved. The H1 receptor agonists, pyridilethylamine and 2-(2 aminoethyl)thiazole, enhanced the electrically evoked twitch responses, but not contractions induced by exogenously-applied norepinephrine and ATP. These effects were prevented by the H1-blocking drugs, mepyramine and phenyramine, but only at high concentrations (10 mumol/l). All these H1-antagonists strongly enhanced muscle response to electrical stimulation. The H2 receptor agonists, dimaprit, amthamine and impromidine, reduced the contractions evoked by field stimulation, but not by exogenously applied norepinephrine and ATP, the effect being antagonised by H2-blocking drugs, ranitidine and famotidine. The H3 receptor agonist, R(alpha)-methylhistamine, reduced the electrically evoked muscle contractions, the effect being not modified by the selective H3-blocking drug, thioperamide, but prevented by famotidine. These data suggest that rat vas deferens contains presynaptic histamine H2 receptors, able to mediate inhibitory effects on the sympathetic transmission, while histamine H3 receptors are apparently not involved. On the contrary, the role of H1 is still unclear, since both agonists and antagonists may have the same effects.

The cardiac activity of the novel histamine H2-receptor agonist amthamine was investigated in a variety of isolated heart preparations from guinea pigs and humans and in the isolated rabbit aorta. Amthamine caused an increase in the sinus rate of spontaneously beating guinea-pig atria (pD2 = 6.72) and in the contractility of the electrically driven guinea-pig papillary muscle (pD2 = 6.17) and of the human atrium (pD2 = 5.38). In all these systems, amthamine behaved as a full agonist with a potency comparable to or slightly higher than that of histamine and 10 times higher than that of dimaprit. The positive effects of amthamine were competitively antagonized by ranitidine which had pA2 values (6.46 and 6.25 in the guinea-pig atria and papillary muscle, respectively) comparable with those calculated against histamine and dimaprit. In the isolated rabbit aorta amthamine was devoid of H1-mediated activities up to 3 x 10(-4) M. These results indicate that amthamine is a potent and selective histamine H2-receptor agonist which can be considered a valuable tool for investigating H2-receptor mediated effects in cardiac tissues.

The new histamine H2 receptor agonist amthamine, [2-amino-5-(2-aminoethyl)-4-methylthiazole], was tested for its activity on gastric acid secretion in different in vivo and in vitro experimental models. Amthamine induced a dose-related increase in acid secretion both in conscious cats with a gastric fistula (ED50 = 0.069 mumol/kg/h) and in anaesthetized rats with a lumen-perfused stomach (ED50 = 11.69 mumol/kg i.v.). In this last preparation the efficacy of amthamine was significantly higher than that of histamine and dimaprit. Amthamine was an effective secretagogue also in the rat isolated gastric fundus, behaving as a full agonist (EC50 = 18.9 mumol/l). In all the experimental models amthamine was more potent than dimaprit (from 3 to 10 fold) and approximately equipotent with histamine, and its effect was competitively antagonized by the histamine H2 receptor antagonists famotidine or ranitidine. Experiments with H1 and H3 receptor antagonists indicated that amthamine is devoid of stimulatory activity at H1 and H3 receptors. The present data indicate that amthamine is a full agonist at histamine H2 receptors and, being more effective and selective than the other compounds of the family, it may represent a good alternative to the other available histamine H2 receptor agonists for the study of gastric acid secretion.

The effect of (R)alpha-methylhistamine (MH) and thioperamide (selective agonist and antagonist respectively of histamine H3 receptors) was examined in conscious gastric fistula dogs to investigate the role of histamine H3 receptors in the control of basal and stimulated gastric acid secretion. Intravenous infusion of MH at 0.3 and 0.6 mumol/kg/h caused a significant reduction of the 2-deoxy-D-glucose (2-DG)-stimulated acid output, maximal inhibition being 60%. The inhibitory effect of MH was counteracted by thioperamide (0.1 mumol/kg/h), which, by itself, did not modify the 2-DG-induced acid secretion. The increase in plasma gastrin levels induced by 2-DG was not significantly affected either by MH or by thioperamide. Under basal conditions MH (0.3 mumol/kg/h) did not induce any significant change in acid secretion and in plasma gastrin levels; by contrast, thioperamide (0.1 mumol/kg/h) produced a significant increase both in acid output and in plasma gastrin. These results suggest that activation of H3 receptors can exert a negative control in stimulated acid secretion in conscious dogs, when cholinergic pathways to acid secretion are activated by 2-DG; moreover, the slight, but significant, stimulatory effect of thioperamide on basal acid output and basal plasma gastrin may be suggestive for a tonic inhibitory role of H3 receptors in the regulation of basal acid secretion, however, a nonspecific effect of this drug cannot be excluded.

A nonlinear and non-local cochlear model has been efficiently solved in the time domain numerically, obtaining the evolution of the transverse displacement of the basilar membrane at each cochlear place. This information allows one to follow the forward and backward propagation of the traveling wave along the basilar membrane, and to evaluate the otoacoustic response from the time evolution of the stapes displacement. The phase/frequency relation of the response can be predicted, as well as the physical delay associated with the response onset time, to evaluate the relation between different cochlear characteristic times as a function of the stimulus level and of the physical parameters of the model. For a nonlinear cochlea, simplistic frequency-domain interpretations of the otoacoustic response phase behavior may give inconsistent results. Time-domain numerical solutions of the underlying nonlinear and non-local full cochlear model using a large number (thousands) of partitions in space and an adaptive mesh in time are rather time and memory consuming. Therefore, in order to be able to use standard personal computers for simulations reliably, the discretized model has been carefully designed to enforce sparsity of the matrices using a multi-iterative approach. Preliminary results concerning the cochlear characteristic delays are also presented.

The present study tested the hypothesis that several residues in Loop 2 of α1 glycine receptors (GlyRs) play important roles in mediating the transduction of agonist activation to channel gating. This was accomplished by investigating the effect of cysteine point mutations at positions 50–60 on glycine responses in α1GlyRs using two-electrode voltage clamp of Xenopus oocytes. Cysteine substitutions produced position-specific changes in glycine sensitivity that were consistent with a β-turn structure of Loop 2, with odd-numbered residues in the β-turn interacting with other agonist-activation elements at the interface between extracellular and transmembrane domains. We also tested the hypothesis that the charge at position 53 is important for agonist activation by measuring the glycine response of wild type (WT) and E53C GlyRs exposed to methanethiosulfonate reagents. As earlier, E53C GlyRs have a significantly higher EC50 than WT GlyRs. Exposing E53C GlyRs to the negatively charged 2-sulfonatoethyl methanethiosulfonate, but not neutral 2-hydroxyethyl methanethiosulfonate, positively charged 2-aminoethyl methanethiosulfonate, or 2-trimethylammonioethyl methanethiosulfonate, decreased the glycine EC50 to resemble WT GlyR responses. Exposure to these reagents did not significantly alter the glycine EC50 for WT GlyRs. The latter findings suggest that the negative charge at position 53 is important for activation of GlyRs through its interaction with positive charge(s) in other neighboring agonist activation elements. Collectively, the findings provide the basis for a refined molecular model of α1GlyRs based on the recent x-ray structure of a prokaryotic pentameric ligand-gated ion channel and offer insight into the structure-function relationships in GlyRs and possibly other ligand-gated ion channels.

The effects of the histamine H2-receptor antagonists ranitidine and famotidine on acetylcholine release have been studied in the guinea pig myenteric plexus longitudinal muscle preparation incubated with [3H]-choline. Ranitidine (3 x 10(-5)-3 x 10(-4) M) dose-dependently increased the resting release of acetylcholine and that evoked by electrical stimulation. The effect was present only in strips perfused with 10(-5) M physostigmine. The effect of ranitidine was inhibited by tetrodotoxin and hexamethonium. Famotidine (10(-5)-3 x 10(-4) M) was totally ineffective in modifying both the resting release and that evoked by field stimulation. Ranitidine did not antagonize the inhibitory effect of oxotremorine, which specifically activates negative feedback mechanisms via presynaptic muscarinic receptors.

Considerable evidence indicates that ethanol acts on specific residues in the transmembrane domains of glycine receptors (GlyRs). In this study, we tested the hypothesis that the extracellular domain is also a target for ethanol action by investigating the effect of cysteine substitutions at positions 52 (extracellular domain) and 267 (transmembrane domain) on responses to n-alcohols and propyl methanethiosulfonate (PMTS) in alpha1GlyRs expressed in Xenopus oocytes. In support of the hypothesis: (i) The A52C mutation changed ethanol sensitivity compared to WT GlyRs; (ii) PMTS produced irreversible alcohol-like potentiation in A52C GlyRs; and (iii) PMTS binding reduced the n-chain alcohol cutoff in A52C GlyRs. Further studies used PMTS binding to cysteines at positions 52 or 267 to block ethanol action at one site in order to determine its effect at other site(s). In these situations, ethanol caused negative modulation when acting at position 52 and positive modulation when acting at position 267. Collectively, these findings parallel the evidence that established the TM domain as a target for ethanol, suggest that positions 52 and 267 are part of the same alcohol pocket and indicate that the net effect of ethanol on GlyR function reflects the summation of its positive and negative modulatory effects on different targets.

We built a model of a GABAA alpha1 receptor (GABAAR) that combines the ligand binding (LBD) and the transmembrane domains (TMD). We used six steps: (1) a four-alpha helical bundle in the crystal structure of bovine cytochrome c oxidase (2OCC) was identified as a template for the TMD of a single subunit. (2) The five pore-forming alpha helices of a bacterial mechanosensitive channel (1MSL) served as a template for the pentameric ion channel. (3) Five copies of the tetrameric template from 2OCC were superimposed on 1MSL to produce a homopentamer containing 20 alpha helices arranged around a funnel-shaped central pore. (4) Five copies of the GABAAR sequence were threaded onto the alpha-helical segments of this template and inter-helical loops were generated to produce the TMD model. (5) A model of the LBD was built by threading the aligned sequence of GABAAR onto the crystal structure of the acetylcholine binding protein (1I9B). (6) The models of the LBD and the TMD were aligned along a common five-fold axis, moved together along that axis until in vdW contact, merged, and then optimized with restrained molecular dynamics. Our model corresponds closely with recently published coordinates of the acetylcholine receptor (1OED) but also explains additional features. Our model reveals structures of loops that were not visible in the cryoelectron micrograph and satisfies most labeling and mutagenesis data. It also suggests mechanisms for ligand binding transduction, ion selectivity, and anesthetic binding.

Background The opioid agonist meperidine has actions, such as antishivering, that are more pronounced than those of other opioid agonists and that are not blocked with nonselective opioid antagonists. Agonists at the alpha(2) adrenoceptors, such as clonidine, are very effective antishivering drugs. Preliminary evidence also indicates that meperidine interacts with alpha(2) adrenoceptors. The authors therefore studied the ability of meperidine to bind and activate each of the alpha(2)-adrenoceptor subtypes in a transfected cell system. Methods The ability of meperidine to bind to and inhibit forskolin-stimulated cyclic adenosine monophosphate formation as mediated by the three alpha(2)-adrenoceptor subtypes transiently transfected into COS-7 cells has been tested. The ability of the opioid antagonist naloxone and the alpha(2)-adrenoceptor antagonists yohimbine and RX821002 to block the analgesic action of meperidine in the hot-plate test was also assessed. The ability of meperidine to fit into the alpha(2B) adrenoceptor was assessed using molecular modeling techniques. Results Meperidine bound to all alpha2-adrenoceptor subtypes, with alpha(2B) having the highest affinity (alpha(2B), 8.6 +/- 0.3 microm; alpha(2C), 13.6 +/- 1.5 microm, P < 0.05; alpha(2A), 38.6 +/- 0.7 microm). Morphine was ineffective at binding to any of the receptor subtypes. Meperidine inhibited the production of forskolin-stimulated cyclic adenosine monophosphate mediated by all receptor subtypes but was most effective at the alpha(2B) adrenoceptor (alpha(2B), 0.6 microm; alpha(2A), 1.3 mm; alpha(2C), 0.3 mm), reaching the same level of inhibition (approximately 70%) as achieved with the alpha2-adrenoceptor agonist dexmedetomidine. The analgesic action of meperidine was blocked by naloxone but not by the alpha 2-adrenoceptor antagonists yohimbine and RX821002. The modeling studies demonstrated that meperidine can fit into the alpha(2B)-adrenoceptor subtype. Conclusion Meperidine is a potent agonist at the alpha2 adrenoceptors at its clinically relevant concentrations, especially at the alpha(2B)-adrenoceptor subtype. Activation of the alpha(2B) receptor does not contribute significantly to the analgesic action of meperidine. This raises the possibility that some of its actions, such as antishivering, are transduced by this mechanism.

There has been rapid progress in molecular modeling of LGICs in recent years. The convergence of improved software for molecular mechanics/dynamics, techniques of chimeric substitution and site-directed mutations, and the first X-ray structures of transmembrane ion channels will make it possible to build reasonable models of neuronal ion channels well in advance of publication of their crystal structures. These models will not only serve as guides for future site-directed mutagenesis, but they will also be a starting point for understanding the dynamics of ion channel gating.

The role of histamine H3-receptors in the control of acetylcholine release from peripheral cholinergic neurons was evaluated in the isolated guinea pig ileum, previously loaded with 3H-choline. When tested in the presence of H1- and H2-blockade, histamine (0.1-100 mumol/l) and (R) alpha-methylhistamine (0.01-1 mumol/l) dose-dependently reduced the electrically-evoked choline outflow, with (R) alpha-methylhistamine being a partial agonist. Selective H3-receptor blocking drugs, thioperamide (0.1 mumol/l) and impromidine (0.1 mumol/l) reversed the histamine-induced inhibitory effect. These data suggest that intestinal cholinergic nerves are endowed with histamine H3-receptors whose activation produces an inhibitory effect upon acetylcholine release. The practical implications of these findings are obvious.

In an attempt to assess the role of histamine H3 receptors in the control of gastric acid secretion, the effects of the selective histamine H3 receptor agonist, (R) alpha-methylhistamine and antagonist, thioperamide were evaluated in the conscious gastric fistula cat under basal conditions and against different stimuli. (R) alpha-methylhistamine (0.05-0.2 mumol/kg/h) was ineffective against spontaneous and dimaprit-induced acid secretion; it also did not reduce significantly pentagastrin-induced acid output, but caused a dose-dependent (0.05-0.1 mumol/kg/h) and significant inhibition of the acid response to 2-deoxy-D-glucose. Thioperamide (0.02-0.04 mumol/kg/h) did not modify spontaneous acid secretion, whereas it evoked a significant enhancement of the acid response to submaximal doses (50 mg/kg i.v.) of 2-deoxy-D-glucose. Thioperamide completely reversed the inhibitory effect of (R) alpha-methylhistamine against 2-deoxy-D-glucose-induced secretion, while leaving unaffected the inhibition induced by somatostatin. These data suggest that histamine H3 receptors may be involved in the control of acid secretion stimulated by indirectly acting secretagogues.

The histamine H(3) receptor shows high degree of stereoselectivity for histamine analogues branched in the side chain. The hypothesis that gastroprotection by (R)-alpha-methylhistamine could be H(3) receptor-mediated was tested by comparing the effect of (R)-alpha-methylhistamine and of (S)-alpha-methylhistamine on ethanol-induced histologic lesions in the rat gastric mucosa. Extensive damage was caused by 60 min exposure to absolute ethanol, 91% of the mucosa examined being damaged. Conversely only 23% of the mucosa was damaged after pretreatment with (R)-alpha-methylhistamine (100 mg/kg i.g.). In the groups pretreated with (S)-alpha-methylhistamine (55.44 and 166.3 mg/kg i.g.) total damage ranged from 77 to 79%, though it was confined to the upper portion of the mucosa. Morphometric analysis of stained intraepithelial mucosubstances revealed that (R)-alpha-methylhistamine pretreatment resulted in an increase in number and volume of surface mucous cells, not evident after (S)-alpha-methylhistamine pretreatment. Scanning electron microscopy confirmed light microscopy evaluations. The two isomers of alpha-methylhistamine differently affect the response of rat gastric mucosa to absolute ethanol and they appear to differ in their influence on surface mucous cells. A basis for interpreting the effects of the two isomers of alpha-methylhistamine rests on the high degree of stereoselectivity of H(3) receptors and on the different affinities of the two isomers for these receptors.

Histamine H2 receptor-mediated responses were examined on cholecystokinin-octapeptide (CCK-8)-precontracted guinea pig gallbladder in vitro, testing histamine and a series of specific histamine H2 receptor agonists and antagonists. Among the antagonists tested, zolantidine and compound SKF 92857 were previously shown to antagonize H2 receptor-mediated responses in the heart, but not in the stomach. Histamine, in the presence of the H2 receptor antagonist mepyramine (10 microM), and the H2 receptor agonists dimaprit, impromidine and amthamine, inhibited CCK-8 (3 nM)-induced contractions in a concentration-dependent fashion, with the following rank orders of potency: impromidine > amthamine > histamine > dimaprit (pD2 values were 6.73 +/- 0.04, 5.44 +/- 0.07, 4.64 +/- 0.04 and 3.71 +/- 0.05, respectively). The maximal relaxation produced by dimaprit was significantly lower than that produced by histamine, as well as by impromidine and amthamine, which behaved as full agonists. All the H2 receptor antagonists examined were able to inhibit amthamine-induced relaxation. Famotidine (pA2 = 7.09 +/- 0.26), zolantidine (pA2 = 6.54 +/- 0.11), compound SKF 92857 (pA2 = 6.58 +/- 0.13) and aminopotentidine (pA2 = 6.86 +/- 0.06) competitively antagonised the amthamine-induced effect, while iodoaminopotentidine produced surmountable antagonism only at low concentrations (1 microM, pA2 = 6.83 +/- 0.21). Finally, the slowly-dissociable antagonist loxtidine caused a non-parallel displacement to the right of the concentration--response curve to amthamine (pKB = 7.55 +/- 0.24), with a significant depression of the maximal response to the agonist, even at the lowest effective concentration (0.3 microM). In conclusion, histamine H2 receptors in guinea pig gallbladder resemble those of the heart, as regards their sensitivity to zolantidine and compound SKF 92857, which, by contrast, were unable to antagonize histamine effects at gastric H2 receptors in different experimental models.

The proton pump inhibitors omeprazole and lansoprazole and the histamine H2 receptor antagonists ranitidine and nizatidine were investigated for their effects on gastric transmucosal potential difference (PD) in the rat, in comparison with the gastroprotective compound sucralfate. Omeprazole (1-3 mg kg-1, i.v.) and lansoprazole (1-3 mg kg-1, i.v.) did not modify basal PD, but significantly reduced (by approx. 50-60%) the drop in PD caused by intragastric administration of acetylsalicylic acid (ASA, 60 mg kg-1). Ranitidine (3-100 mg kg-1, i.v.) and nizatidine (10-30 mg kg-1, i.v.) behaved similarly to proton pump inhibitors, being ineffective on basal PD, while significantly reducing the effect of ASA. The antisecretory compounds did not change basal pH values. Sucralfate (0.5-1.5 g kg-1 intragastrically) caused a slight increase (approx. 20%) of basal PD and a dose-dependent reduction of ASA-induced fall in PD, with a maximum effect (65% reduction) comparable to that caused by the antisecretory agents. These results showed that ASA-induced disruption of the mucosal barrier can be reduced to the same extent by various antiulcer drugs, irrespective of their effects on gastric acid secretion.

1. The histamine H2 receptor agonists, dimaprit, impromidine, amthamine, and several dimaprit- and impromidine-analogues were investigated for their spasmolytic activity on the guinea pig duodenum, precontracted with acetylcholine or KCl. 2. Almost all the H2 receptor agonists exerted a histamine H2 receptor-independent muscle relaxation, which was more evident on acetylcholine- than on KCl-precontracted preparations. 3. The relaxing activity of these compounds was independent of inhibitory receptors, like beta-adrenergic, GABA-ergic, serotoninergic, etc. Similarly, modifications of cyclic nucleotide metabolism and nitric oxide production did not appear to be involved. 4. The behavior of histamine H2-receptor agonists was shared only by the Na+-blocker procaine, the intracellular Ca2+-antagonist ruthenium red and, at least in terms of efficacy, by the protein kinase C inhibitor, chelerithrine. 5. This spasmolytic effect is probably due to an impairment of receptor-mediated depolarization at the plasma membrane level and/or an inhibitory activity on the protein kinase C-dependent activation of the contractile machinery. 6. Finally, our findings suggest that the histamine H2 receptor-independent muscle relaxation is a general feature shown by H2 receptor agonists endowed with different chemical structure and the putative spasmolytic "receptor" prefers a (substituted) thiazole over a (substituted) imidazole.

A number of ranitidine analogues in which the diamino-1,2,5-thiadiazole 1-oxide substructure bearing alkyl chains of different length is present as the urea equivalent group, were synthesised and studied for their lipophilic and H2 antagonist properties. Derivatives which displayed a logP≤3 behaved as competitive antagonists of histamine at H2 receptors present on guinea pig right atrium. The remaining more lipophilic members of the series showed an insurmountable antagonism not completely reversible after prolonged washing. A binding study suggested that an increase in the length of alkyl chain gave rise to hydrophobic interactions with the receptor which were responsible for the apparent irreversible H2 antagonism shown by the higher homologues of the series.

The effect of the beta3-adrenoceptor agonist [ N-[(2S)-7-ethoxycarbonyl-methoxyl-1,2,3,4-tetrahydronaphth-2-yl] (2R)-2-(3-chloro-phenyl)2-hydroxyethanamine hydrochloride] (SR58611A) on gastric acid secretion was investigated in conscious cats with a gastric fistula. Intravenous infusion of SR58611A (0.3-3 micromol/kg/h) caused a dose-dependent inhibition of the acid secretion stimulated by 2-deoxy-D-glucose (2DG), with a maximum reduction by 45%. The secretory effect of the histamine H2-receptor agonist dimaprit only tended to be reduced by SR58611A (3 micromol/kg/h). The inhibitory effect of SR5861 IA was not modified by the non selective beta1- and beta2-adrenoceptor antagonist propranolol (1.5 micromol/kg i.v.), but it was prevented by bupranolol (10 micromol/kg i.v.), a drug endowed with beta3-antagonistic properties. Both antagonists blocked the inhibitory effect of the beta2-adrenoceptor agonist clenbuterol (0.1 micromol/kg/h) on 2DG-induced acid secretion. These findings suggest that compound SR58611A inhibits gastric acid secretion in the conscious cat through activation of beta3-adrenoceptors insensitive to propranolol.