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The effect of anthelmintic treatment of pigs on the embryonation and infectivity of Ascaris suum eggs isolated from expelled worms was investigated. Four groups of two naturally infected pigs were dosed with albendazole, pyrantel pamoate, ivermectin or piperazine dihydrochloride, respectively. Following worm expulsion, the eggs were removed from the uteri of female worms and embryonated in sulphuric acid. The infectivity of the embryonated eggs was tested through mouse inoculation. Egg development appeared normal in cultures from worms of the piperazine. pyrantel and ivermectin treated groups. In the albendazole cultures, egg development was largely arrested at the one-cell stage (81%). Where development occurred, irregular cell division was observed and only 7% of the eggs in the culture developed into fullgrown larvae. Following mouse inoculation with 2500 embryonated eggs, significantly lower lung larval counts on day 8 post inoculation (p.i.) were observed for mice in the piperazine and pyrantel treated groups (P < 0.01) compared to untreated controls. The larvae that developed in the eggs from ivermectin and albendazole treated groups appeared fully infective for mice. It was concluded that ovicidal activity of albendazole in vivo inhibits subsequent A. suum egg development in vitro; albendazole is, therefore, not suitable to obtain worms for egg embryonation to produce experimental inoculums. The anthelmintic treatment of pigs with ivermectin had only a limited effect on both embryonation and infectivity of A. suum eggs isolated from expelled worms.

The anthelmintic invermectin has a number of effects on nematodes which result in changes in behaviour, particularly locomotion, including paralysis and an inhibition of feeding. This paper describes the application of an in vitro pharmacological approach to further delineate the action of ivermectin on feeding behaviour. Contraction of Ascaris suum pharyngeal muscle was monitored using a modified pressure transducer system which detects changes in intrapharyngeal pressure and therefore contraction of the radial muscle of the pharynx. The pharynx did not contract spontaneously. However, serotonin (5-HT, 100 microM) stimulated rhythmic contractions and relaxations (pumping) at a frequency of 0.5 Hz. gamma-Aminobutyric acid (GABA) and glutamic acid inhibited the pumping elicited by 5-HT. The duration of inhibition was concentration dependent (1-1000 microM) with a threshold of 1 microM and 10 microM respectively (n = 8). Ivermectin also inhibited pharyngeal pumping (1-1000 nM). At lower concentrations, ivermectin (1-10 pM) potentiated the GABA and glutamate inhibition, so that inhibition occurred at concentrations which were below threshold in the absence of ivermectin. These data provide evidence that the pharynx is a site for the action of ivermectin. Thus interruption of pharyngeal processes such as, feeding, regulation of hydrostatic pressure and secretion may provide a new site of anthelmintic action.

AF3 (AVPGVLRFamide) and AF4 (GDVPGVLRFamide) are endogenous RFamide-like peptides isolated from the parasitic nematode Ascaris suum. Here the actions of these peptides on the somatic musculature of Ascaris have been investigated and compared to the action of acetylcholine (ACh), the excitatory transmitter at the neuromuscular junction. ACh, AF3 and AF4 contracted muscle with EC50S of 13 +/- 1 microM, 24 +/- 6 nM and 37 +/- 2 nM, respectively (n = 6). The muscle cells were depolarized by ACh (3 microM; 5.2 +/- 0.4 mV, n = 42), AF3 (1 microM; 2.6 +/- 0.3 mV, n = 19) and AF4 (1 microM; 3.3 +/- 0.4 mV, n = 19). EC50S were 681 +/- 329 nM (AF3) and 901 +/- 229 nM (AF4), but an estimate could not be made for ACh due to muscle contraction at concentrations greater than 10 microM. The depolarization to 3 microM ACh was abolished by the nicotinic receptor antagonist mecamylamine (10 microM; n = 5) but the responses to the peptides were not (111 +/- 7% and 108 +/- 17% with respect to control; n = 5). The depolarization elicited by ACh was reduced to a greater extent by a 50% reduction in extracellular Na+ concentration than the response to AF3 and AF4 (P < 0.02). Cobalt was more effective at blocking the AF3 and AF4 depolarizations than those to ACh. These observations suggest that AF3 and AF4 contract Ascaris muscle without an action at the Ascaris nicotinic receptor. Furthermore, the ionic mechanism through which AF3 and AF4 depolarize Ascaris muscle is different from that for ACh. ACh, AF3 and AF4 were also found to contract Ascaridia galli somatic muscle with EC50S of 13 +/- 3 microM, 721 +/- 236 nM and 371 +/- 177 nM, respectively (n = 7). The muscle cells were depolarized by ACh (EC50 = 14 +/- 5 microM, n = 5), AF3 (EC50 = 5 +/- 3 microM, n = 4) and AF4 (EC50 = 10 +/- 5 microM, n = 4). Therefore the response to these peptides is not unique to Ascaris and they may subserve a functional role in the motor nervous system of parasitic nematodes.

The in vitro activity of root-tuber-peel extract of Flemingia vestita, an indigenous plant consumed by the natives in Northeast India, was tested against helminth parasites. Live parasites (nematode: Ascaris suum from pigs, A. lumbricoides from humans, Ascaridia galli and Heterakis gallinarum from domestic fowl; cestode: Raillietina echinobothrida from domestic fowl; trematode: Paramphistomum sp. from cattle) were collected in 0.9 % physiological buffered saline (PBS) and maintained at 37 +/- 1 degrees C. In vitro treatment of the parasites with the crude extract (50 mg/ml) in PBS revealed complete immobilization of the trematode and cestode in about 43 and 20 min, respectively. However, the cuticle-covered nematodes did not show any change in physical activity and remained viable even after a long period of exposure to the extract. Exposure of R. echinobothrida to genistein (0.5 mg/ml), an active principle isolated from the root-tuber peel, caused spontaneous loss of movement (paralysis) in 4.5 h, which was slower than the time required for praziquantel, the reference flukicide and cestodicide. The treated parasites showed structural alteration in their tegumental architecture. This study suggests the vermifugal activity of this plant extract against trematodes and cestodes.

Isolated muscle bags from the parasitic nematode Ascaris suum were prepared by collagenase treatment and dissection. Single bags were mounted in a V-shaped plastic pipette for voltage clamp application and intra- and extracellular perfusion. With 'physiological' intra- and extracellular solutions, depolarizing voltage steps from near the normal resting membrane potential, -40 mV, produced in leak-corrected currents, a slowly activating outward current at potentials more positive than -20mV. At the end of the depolarizing pulse there was a slow inward tail current with a reversal potential near -20mV. Hyperpolarizing voltage steps produced an outward current relaxation and an outward tail current with the same reversal potential. The observations can be explained by the presence in the bag of a non-selective cation channel current, Ibcat, that activates spontaneously at the holding potential; depolarization increases opening of the channel and hyperpolarization decreases opening. Bath-applied acetylcholine in concentrations greater than 10(-7) M produced an increase in the amplitude of Ibcat. The effect of acetylcholine was not antagonized or prevented by 100 microM tubocurarine, suggesting the presence of a non-nicotinic acetylcholine receptor. Atropine (100 microM) had no detectable influence on the effect of acetylcholine but the FMRFamide peptide, PF1, in concentrations > 1 microM, reduced the amplitude of Ibcat. Ibcat was maintained when Cs+ was used to replace intra- and extracellular cations, showing that the channels were permeable to Cs+. It is concluded that the bag membrane possesses a slow voltage-activated non-selective cation channel current, Ibcat. The effect of acetylcholine in the presence of nicotinic antagonist indicates the presence of non-nicotinic acetylcholine receptors on the bag membrane. The effect of PF1 indicated the presence of PF1 receptors on the bag membrane.

Hydrated lime was lethal to the strain of Salmonella typhimurium (Sk 14/39) after 60 min of exposure. In the control without addition of hydrated lime this strain was still viable after 168 hours, counting 6.1 x 10(5) pathogens/l ml sludge. 168-hr disinfection of primary sludges with 10 g/l hydrated lime showed no significant reduction in the viability of Ascaris suum eggs. In three experiments, the number of viable eggs was reduced only by 3.6%. Indicator microorganisms, except psychrophilic ones that survive for only 24 hr, were destroyed after 60 min of exposure. The temperature of stabilized sludges did not vary considerably during experiments, ranging between 21 and 25 degrees C. With the addition of Ca(OH)2, sludge pH increased to the values for COD, organic matters and total nitrogen were reduced throughout the experiments. The values for sludge dry residues remained unchanged.

1. We have investigated activation and block, by the tetrahydropyrimidine anthelmintic, morantel, of nicotinic-acetylcholine receptor (AChR) currents in membrane vesicles isolated from somatic muscle cells of the nematode parasite Ascaris suum. Standard single-channel recording techniques were employed. Morantel in the pipette (6 nM to 600 microM), activated single nicotinic AChR currents. 2. Kinetic properties of the main-conductance state of morantel-activated currents were investigated in detail throughout the concentration range, 0.6 microM to 600 microM. Open-time distributions were best fitted by a single exponential. Mean open-times were slightly voltage-dependent, increasing from 0.9 ms at +75 mV to 1.74 ms at -75 mV in the presence of 0.6 microM morantel. At low concentrations, closed-time distributions were best fitted by the sum of two or three exponential components. 3. As the concentration of morantel was increased (100-600 microM), fast-flickering open channel-block was observed at positive potentials, even though morantel, a cation, was only present at the extracellular surface of the membrane. The block rate was dependent on morantel concentration and both block rate and duration of block increased as the potential became less positive. A simple channel-block mechanism did not explain properties of this block. 4. At negative potentials, as the morantel concentration increased, a complex block was observed. With increases in morantel concentration two additional gap components appeared in closed-time distributions: one was short with a duration (approximately 13 ms) independent of morantel concentration; the other was long with a duration that increased with morantel concentration (up to many minutes). In combination, these two components produced a marked reduction in probability of channel opening (Po) with increasing morantel concentration. The relationship between the degrees of block and morantel concentration had a Hill coefficient of 1.6, suggesting the involvement of at least two blocking molecules. The data were analysed by use of a simple sequential double block kinetic model.

The decoction of the stem bark of Zanthoxylum liebmannianum (Engelm.) P. Wilson (Rutaceae) decreased the count of intestinal nematode eggs in naturally infected sheep. In addition, the chloroformic extract was toxic to Ascaris suum. Fractionation of the organic extract guided by the Ascaris suum lethality test led to the isolation of alpha-sanshool (LC50 = 83.4 x 10(-5)M) as the only active compound. On the other hand, alpha-sanshool induced tonic-clonic seizures when it was injected intraperitoneally to mice. This finding could be a warning regarding the potential toxicity of this plant.

The effect of albendazole therapy on adult Ascaris suum was examined using transmission electron microscopy. The drug induced prominent ultrastructural changes which included the presence of necrotic dense bodies, myelin whorls which appeared to represent various stages of lysosomal formation and autolysis, disruption and erosion of the microvilli. The effects were mainly confined to the central region of the intestinal epithelial cells.

We examined the effect of PF1022A, one of the gabergic anthelmintics newly developed in Japan, on gamma-aminobutyric acid (GABA) receptors using a radioligand binding technique in isolated membrane preparations of the nematode Ascaris suum. Membrane protein was prepared from the homogenate of somatic muscle cells after ultracentrifugation. In addition to the basic binding of [2,3-3H-(N)]-GABA, the radioligand [methyl-3H]-bicuculline is used to identify the GABAA receptor, whereas [butyl-4-3H]-baclofen is employed for GABAB receptor sites. The dissociation constants (Kd values) and the maximal numbers of binding sites (Bmax values) from Scatchard plotting for GABA receptors are close to those obtained in mammalian brain. PF1022A displaced in a concentration-dependent way the binding of [2,3-3H(N)]-GABA and [methyl-3H]-bicuculline as did other specific gabergic agents. In addition, PF1022A decreased the binding of [butyl-4-3H]-baclofen at a higher concentration, although this binding did not represent GABAB sites. In a comparison of the inhibition constants (Ki values) of PF1022A with those of other agents, it is conclusive that PF1022A bound with GABA receptors. A direct effect of PF1022A on GABA receptors can thus be postulated.

Three groups of anthelmintic drugs act directly and selectively on muscle membrane receptors of parasitic nematodes. These groups of anthelmintics are: (1) The Nicotinic Agonists (levamisole, pyrantel, morantel and oxantel) that act on acetylcholine receptors of nematode somatic muscle; (2) The GABA Agonist, piperazine, that acts on nematode muscle GABA receptors; and (3) The Avermectins that open glutamate gated Cl- channels on nematode pharyngeal muscle. The electrophysiology and pharmacology of muscle and neuromuscular transmission the nematode parasite, Ascaris suum, is outlined and effects of anthelmintics that interfere with transmission described. Resistance to anthelmintics has appeared in some parasitic nematodes but the mechanisms of this resistance remain to be determined.

The development of Ascaris suum eggs maintained in the culture containing moxidectin (Cydectin, Cyanamid) in concentration 1, 5, 25, and 50 micrograms/ml was studied. The abnormalities and slowing down of the rate of eggs development, depending on the drug concentration, were observed. Exposure of eggs to moxidectin in concentration 1 and 5 microgram/ml resulted in one- or two-week delay of development. In the higher concentration of moxidectin (25 micrograms/ml) only 18% of eggs became invasive. In the presence of 50 micrograms/ml of the drug only few eggs developed to invasive stage after 7 weeks. The development of embryons was stopped more often in the blastula or gastrula stage. The drug's solvent in the highest concentration restricted the development of Ascaris eggs by about 10%. Unembryonated eggs of the worm appeared to be unaffected by 50 micrograms/ml of moxidectin treatment lasting 1-4 days, but for slowing down a little the development rate. The same concentration of the drug in the culture during the first four days of development resulted in 20% reduction of invasive stage in comparison to the control.

We investigated the effect of DL-buthionine-S,R-sulfoximine (BSO), a selective glutathione (GSH)-depleting agent, on the GSH synthesis of Ascaris suum. The GSH concentrations of the reproductive and muscle tissues of A. suum were determined to be 8.5 +/- 0.3 and 14.3 +/- 1.3 (n = 3) nmol/mg protein, respectively. After treatment of the parasites with 10 microM BSO for 24 h, the GSH content of the reproductive tissue of A. suum was totally depleted as compared with that of untreated controls. However, the GSH levels of the muscle tissue were reduced to only 50% after treatment of the worms for 24 h with 10 microM BSO. Exogenous GSH had no significant effect on the GSH level of the parasites when the worms were incubated for 4 h in RPMI 1640 medium supplemented with 1 mM GSH. In the presence of exogenous GSH, BSO was less effective in depleting the GSH levels of the parasites, which may indicate that the parasites can replenish their GSH levels. GSH depletion, which has been discussed as being therapeutically effective when normal and tumor cells or parasites have markedly different requirements for GSH, may have applications in the development of drugs against nematode infections.

PF4 has previously been shown to have potent inhibitory effects on myoactivity of somatic muscle strips from the nematode. Ascaris suum. This study examined the bioactivity and metabolic stability of position 2- and position 5-modified analogues of PF4. Although the analogues [Leu5]PF4,[Ala2]PF4, [Gly2]PF4, [Ala2,Leu5]PF4, and [Gly2,Leu5]PF4 all had qualitatively similar inhibitory effects on A. suum somatic muscle strips, their effects were quantitatively distinguishable and had the order of potency: PF4 = [Leu5]PF4 > > [Ala2]PF4 = [Ala2,Leu5]PF4 > > [Gly2]PF4 = [Gly2,Leu5]PF4, Leu5 for Ile5 substitutions in PF4 did not alter the activity of this peptide: however, Gly2/Ala2 for Pro2 substitutions reduced, but did not abolish, peptide activity. Peptide stability studies revealed that [Gly2]PF4(2-7) and -(3-7) and [Ala2]PF4(2-7), -(3-7), and -(4-7) fragments were generated following exposure to A. suum somatic muscle strips. However, the parent peptide (PF4) was not metabolized and appeared to be resistant to the sequential cleavages of native aminopeptidases. Observed analogue metabolism appeared to be due to the activity of released aminopeptidases as identical fragments were generated by incubation in medium that had been exposed to somatic muscle strips and from which the strips had been removed prior to peptide addition. It was found that the muscle stretching and bath mixing characteristics of the tension assay led to more effective release of soluble enzymes from muscle strips and thus greater peptide degradation. These studies reveal that Pro2 in PF4 is not essential for the biological activity of this peptide; however, it does render the peptide resistant to the actions of native nematode aminopeptidases.

Larvae of Ascaris suum (L2) newly hatched from eggs with sodium hypochlorite, were placed (2000 larvae per 2 ml) of culture in EAGLE's medium, containing 10% calve serum or without it. Moxidectin (Cydectin) was introduced into medium in concentrations: 5, 10, 25 and 50 micrograms/ml. The cultures were incubated for 3 days, and there were controlled every 12 hours. The effect of drug on survival of larvae was slightly expressed. After 3 days survival rates were 87, 81, 80 and 78% in medium with serum, respectively to moxidectin concentrations. The lethality of larvae was higher in medium without serum, and amounted to 17, 23, 29 and 31% in comparison with control probe after 72 hours. Adult Ascaris were placed on ARS medium with glucose (0.1%) containing moxidectin in concentrations 1, 5, 50 and 100 micrograms/ml. The worms' condition was examined every day based on motility and turgor of their body. After 14 days of incubation in control probe 50% worms were alive, but their vitality was reduced. The behaviour of Ascaris in the presence of 50 micrograms/ml moxidectin was similar to those from the control. Only the highest concentration of drug (100 micrograms/ml) was lethal in 100% on the 8th day. The lower moxidectin concentrations (1 and 5 micrograms/ml) were not lethal to adult worms, they had even the positive effect on survival rate and condition of adult Ascaris. The eggs laid by females which were maintained in culture with drug were collected. There were no disturbances in their future development.

The pharyngeal component of the enteric nervous system of the parasitic nematode, Ascaris suum exhibits immunoreactivity for serotonin (5-hydroxytryptamine or 5-HT) and for FMRFamide-like peptides. This paper describes the application of an in vitro pharmacological approach to investigate the functional role of 5-HT and FMRFamide-like peptides. The pharyngeal pumping behaviour of Ascaris suum was monitored using a modified pressure transducer system which measures pharyngeal pressure changes and therefore pumping. The pharynx did not contract spontaneously; however, 5-HT (10-1000 microM) stimulated pumping at a frequency of 0.5 Hz. FMRFamide had no apparent effect on pharyngeal pumping. The native nematode FMRFamide-related peptide (FaRP), KSAYMRFamide inhibited the pumping elicited by 5-HT. The duration of inhibition was dose-dependent (0.1-1000 nM) with a threshold of 0.1 nM. In 4 preparations, the inhibition of the pharyngeal muscle was preceded by an initial excitation and increase in the amplitude of pharyngeal pressure changes. The pharynx is involved in various nematode processes, including feeding, regulation of hydrostatic pressure and excretion. The role of 5-HT and KSAYMRFamide in the pharyngeal function of nematodes is discussed.

The structure-activity relationships of 35 novel derivatives of 2-(carboxypropyl)-3-amino-4-methyl-6-phenyl pyridazine (SR 95103) were examined as gamma-aminobutyric acid (GABA) antagonists in the flap preparation of the parasitic nematode, Ascaris suum, using a two-microelectrode current-clamp technique. All but one of the potent antagonists displaced GABA dose-response curves to the right without reduction in the maximum response. The dissociation constants of the more potent competitive antagonists were described using a model which assumed that two molecules of GABA were required to open the ion channel but that only one molecule of antagonist acted on each ion channel. By exploring the structure-activity relationship, the potency of the antagonist was increased from a KB of 64 microM for SR 95103 to a KB of 4.7 microM for NCS 281-93 (2-(3-carboxypropyl)-3-amino-4-phenylpropyl-6-phenyl pyridazine).

Electrophysiological measurements demonstrate that an electrochemical potential exists across the body wall of parasitic nematodes. The ionic dependence of this transmural electrical potential (Etm) in the gastrointestinal nematode Ascaris suum was investigated using conventional electrophysiological techniques. Etm recorded from intact A. suum maintained in artificial pseudocoelomic fluid (APF) was -40 +/- 12 mV. This potential was more sensitive to external acetate than to Na+, K+, or Cl-, although elimination of most Na+ from the medium significantly hyperpolarized the body wall. An Ussing chamber and isolated segments of A. suum body wall were used to delineate the barrier characteristics of the individual components of the body wall: the cuticle and the inward- and outward-facing membranes of the hypodermis. The cuticle (i.e., muscle and hypodermis scraped away) is highly permeable to both inorganic and organic ions, with the rank-order of permeability among ions tested being K+ > Na+ = Cl- > acetate- > gluconate-. The inward- and outward-facing membranes of the hypodermis were more polarized than the body wall complex, exhibiting potentials in APF of -47.6 +/- 6 mV (Ei) and -74.9 +/- 7 mV (Eo) versus -26 +/- 8 mV (Etm for isolated body wall segments), respectively. The electrical potential across the hypodermal membranes became depolarized when high K+ medium or low acetate medium was added to the muscle side, but not when added to the cuticle side of isolated body wall segments. Etm, Eo, and Ei were unaffected by reduction of Na+, K+, or Cl- concentrations in the recording medium. All three potentials, however, became markedly depolarized when the temperature of the incubation medium was reduced. These results indicate that the cuticle/hypodermis complex of A. suum is differentially permeable to both inorganic and organic ions and suggest that active transport of ions or outward diffusion of metabolic end-products contributes extensively to the maintenance of transmural electrochemical gradients.

The studies were carried out on twenty newborn piglets. They were divided into four groups. The groups no 3 and no 4 were given intragastric 0.18% HCl from the 3th day of experiment. The groups no 2 and no 4 were infected on the 7th day with 10,000 invasive eggs of Ascaris suum. The presence of A. suum larvae in the lungs and liver was examined after one week lasting invasion by Baermann method. The total acidity in the gastric content was measured. The activity of alpha-amylase, lipase and proteases was determined in the extracts from pancreas and in the contents of stomach, duodenum and jejunum. The level of pepsinogens and alpha-amylase in the animals serum was studied. The intensity of Ascaris invasion was slightly higher in the group which was given HCl than in the infected group without HCl. The activity of digestive enzymes in the both groups was similar. Only in the stomach content from the 4th group the activity of pepsin was higher (p < 0.05), and alpha-amylase and lipase were lower (p < 0.01) than in the 2nd and in the 3th group. The level of pepsinogens was always lower and alpha-amylase higher in the serum of infected animals than in uninfected groups.

The anthelmintic pyrantel is believed to act as an agonist at acetylcholine receptors on somatic muscle from the parasite Ascaris suum. This study aimed to confirm this mode of action of pyrantel. Single-channel recordings from muscle vesicles formed from the extrasynaptic region of the bag of somatic muscle cells of Ascaris suum were made using the patch-clamp technique. Pyrantel (0.03-100 microM) activated cation-selective channels with at least 2 conductance levels: main conductance 41 +/- 2.04 pS (mean +/- S.E., n = 28), smaller conductance 22.4 +/- 0.34 pS (mean +/- S.E., n = 8). The current/voltage plots showed a linear relationship. Detailed kinetic analysis revealed that activation of the receptor by pyrantel resulted in at least 2 distinct open and burst states and at least 3 distinct closed states. The mean open time of the channel, with 0.1 microM pyrantel, was 1.53 +/- 0.22 ms (mean +/- S.E., n = 7) at -75 mV. We have previously shown that acetylcholine activated channels with similar properties to the pyrantel-activated channels (Pennington, A.J. and R.J. Martin, 1990, J. Exp. Biol. 154, 201) confirming that pyrantel is an acetylcholine agonist. With high concentrations (100 microM) of pyrantel a sequence of rapid openings and closings of the channel was observed, indicating the presence of an open channel block. Previous experiments have shown that the anthelmintic levamisole, which also acts as an acetylcholine agonist on this preparation, induced channel block at hyperpolarised potentials with high concentrations (Robertson, S.J. and R.J. Martin, 1993, Br. J. Pharmacol. 108, 170). A comparison is made of the actions of the 3 agonists pyrantel, levamisole and acetylcholine at the nicotinic receptor in Ascaris muscle, and implications for the therapeutic use of the compounds are discussed.

In nematodes, FMRFamide-related peptides (FaRPs) have been structurally characterised from the parasite, Ascaris suum, and from two free-living species, Panagrellus redivivus and Caenorhabditis elegans. While both FaRPs isolated from P. redivivus (PF1 and PF2) have been identified in C. elegans, the two heptapeptides isolated from A. suum (AF1 and AF2) have until recently been considered unique to this parasitic species. We have recently isolated AF2 from P. redivivus and, during this study, an additional novel heptapeptide amide, Lys-Ser-Ala-Tyr-Met-Arg-Phe amide (KSAYMRFamide), was structurally characterised. A synthetic replicate of this peptide induced a rapid concentration-dependent muscle tension increase in an isolated. A. suum somatic muscle preparation, with a threshold of approximately 0.1 microM. These data suggest that the complement of FaRPs in parasitic and free-living nematodes may not be as radically different as preliminary studies would suggest, and that the absence of AF1, AF2 and KSAYMRFamide on the C.elegans FMRFamide-related peptide gene (flp-1) may imply the presence of at least two different FaRP genes in nematodes.

The binding of tritiated mebendazole, a benzimidazole anthelmintic, to tubulin derived from intestine, body wall muscle, and reproductive system of adult Ascaris suum was examined and compared. Mebendazole binding was resolved into specific and nonspecific binding and the binding affinity (Ka) and maximum binding at infinite ligand concentration (Bmax) determined. Electron microscopy was performed to assess the tubulin in various tissues of A. suum quantitatively by observing the presence of microtubules. Total binding was highest in intestine followed by body wall muscle. It was least in the reproductive system. The intestine demonstrated greater specific binding per milligram of protein than the body wall muscle. However, in the reproductive system extract, high affinity binding was not detected. After correction for nonspecific binding of ligand, the results indicated that the Bmax of mebendazole for the tubulin of A. suum intestine was about 3-fold higher than for that of body wall muscle. The Ka of mebendazole for intestinal tubulin was similar to that for body wall muscle. Electron microscopy of A. suum tissues demonstrated that the tubulin content decreased from the intestine through the body wall muscle to the reproductive system. Differences in tubulin content from different tissues may determine the selective sensitivity of these tissues to benzimidazole attack.

PF1 (SDPNFLRFamide) is a FMRFamide-like peptide extracted from the free-living nematode Panagrellus redivivus. Here we show that this peptide causes a hyperpolarization of somatic muscle cells of the parasitic nematode Ascaris suum and a relaxation of the somatic muscle strip preparation. We have assessed whether or not the relaxation of Ascaris dorsal muscle strip by PF1 is due to (i) inhibition of the release of the excitatory neuromuscular junction transmitter acetylcholine (ACh), (ii) potentiation of the release of the inhibitory neuromuscular junction transmitter gamma-aminobutyric acid (GABA) or (iii) a direct inhibitory action of the peptide on the muscle cells. Under the experimental conditions described here, tonic ACh release does not seem to be involved in determining the resting membrane potential or resting tone of the Ascaris dorsal muscle strip and thus inhibition of tonic ACh release is unlikely to explain the relaxation elicited by the peptide. Furthermore, PF1 (100 nM-1 microM) inhibited the contraction of the muscle strip elicited by bath application of ACh, suggesting either a direct inhibitory action of the peptide on the muscle cells or a potentiation of GABA release. In electrophysiological experiments, the reversal potential for the PF1 hyperpolarization was not the same as that for GABA. Thus, PF1 hyperpolarizes Ascaris muscle by a mechanism that does not involve stimulation of GABA release from inhibitory pre-synaptic terminals.

Ivermectin has been shown to increase chloride conductances of invertebrate cells. On the muscle cells of the parasitic nematode Ascaris, ivermectin acts as both a GABA receptor antagonist and a chloride channel opener. In this study, ion-sensitive microelectrodes were used to investigate the effect of ivermectin on intracellular Cl- concentration of the somatic muscle bag cells of Ascaris suum. Incubation of muscle cells with ivermectin (10 microM in 1% dimethyl sulphoxide vehicle for 60 min) increased intracellular Cl- by 2.9 mM or 15% compared to controls (P < 0.01, n = 6).

Some anthelmintic drugs interfere selectively with nematode neuromuscular transmission. These drugs include: the nicotinic agonists, e.g. levamisole, the gamma-amino butyric acid agonist piperazine, and the avermectins which open Cl- channels. The physiology and pharmacology of neuromuscular transmission in nematodes is reviewed and the actions of antinematodal drugs which interfere with the transmission described. The results of experiments on the large porcine-intestinal nematode parasite, Ascaris suum, form the basis of the account presented but experiments on other nematodes suggest that these observations may be generalized. Results of some experiments on the small free living nematode Caenorhabditis elegans are also included.

1. The patch-clamp technique was used to examine levamisole-activated channels in muscle vesicles from Ascaris suum. Cell-attached and isolated inside-out patches were used. 2. Levamisole (1-90 microM), applied to the extracellular surface, activated channels which had apparent mean open-times in the range 0.80-2.85 ms and linear I/V relationships with conductances in the range 19-46 pS. Ion-replacement experiments showed the channels to be cation selective. 3. The kinetics of the channels were analysed. Generally open- and closed-time distributions were best fitted by two, and three exponentials respectively, indicating the presence of at least two open states and at least three closed states. The distributions of burst-times were best-fitted by two exponentials. 4. Channel open- and burst-times were voltage-sensitive: at low levamisole concentrations (1-10 microM), they increased with hyperpolarization. At higher concentrations of levamisole (30 microM and 90 microM) flickering channel-block was observed at hyperpolarized potentials. Using a simple channel-block model, values for the blocking dissociation constant, KB were determined as 123 microM at -50 mV, 46 microM at -75 mV and 9.4 microM at -100 mV. 5. At the higher concentration of levamisole (30 microM and 90 microM) long closed-times separating 'clusters' of bursts were observed, at both hyperpolarized and depolarized membrane potentials and this was interpreted as desensitization.