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Abstract: Aquaporin-4 (AQP4) water channels are expressed strongly in glial cells, where they play a role in brain water balance, neuroexcitation, and glial cell migration. Here, we investigated a proposed new role of AQP4 in facilitating cell–cell adhesion. Measurements were made in differentiated primary glial cell cultures from wild-type versus AQP4 knockout mice as well as in null versus AQP4-transfected L-cells, a cell type lacking endogenous adhesion molecules, and in null versus AQP4-transfected Chinese hamster ovary (CHO)-K1 cells and Fisher rat thyroid cells. Using established assays of cell–cell adhesion, we found no significant effect of AQP4 expression on adhesion in each of the cell types. As a positive control, transfection with E-cadherin greatly increased cell–cell adhesion. High-level AQP4 expression also did not affect aggregation of plasma membrane vesicles in a sensitive quasi-elastic light-scattering assay. Further, we found no specific AQP4 binding of a fluorescently labeled oligopeptide containing the putative adhesion sequence in the second extracellular loop of AQP4. These data provide evidence against involvement of AQP4 in cell–cell adhesion. [Copyright &y& Elsevier]

Abstract: The thiazolidinone 3-[(3-trifluoromethyl)phenyl]-5-[(4-carboxyphenyl)methylene]-2-thioxo-4-thiazolidinone (CFTRinh-172) inhibits cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel conductance with submicromolar affinity and blocks cholera toxin-induced intestinal fluid secretion. Fifty-eight CFTRinh-172 analogs were synthesized to identify CFTR inhibitors with improved water solubility, exploring modifications in its two phenyl rings, thiazolidinone core, and core-phenyl connectors. Greatest CFTR inhibition potency was found for 3-CF3 and polar group-substituted-phenyl rings, and a thiazolidinone core. Two compounds with ∼1μM CFTR inhibition potency and solubility >180μM (>10-fold more than CFTRinh-172) were identified: Tetrazolo-172, containing 4-tetrazolophenyl in place of 4-carboxyphenyl, and Oxo-172, containing thiazolidinedione in place of the thiazolidinone core. These water soluble thiazolidinone analogs had low cellular toxicity. The improved water solubility of Tetrazolo- and Oxo-172 make them potential lead candidates for therapy of secretory diarrheas and polycystic kidney disease. [Copyright &y& Elsevier]

Abstract: The aquaporins (AQPs) are integral membrane proteins whose main function is to transport water across cell membranes in response to osmotic gradients. At the ocular surface, AQP1 is expressed in corneal endothelium, AQP3 and AQP5 in corneal epithelium, and AQP3 in conjunctival epithelium. AQPs are also expressed in lens fiber cells (AQP0), lens epithelium (AQP1), ciliary epithelium (AQP1, AQP4) and retinal Müller cells (AQP4). Mutations in AQP0 produce congenital cataracts in humans. Analysis of knockout mice lacking individual AQPs suggests their involvement in maintenance of corneal and lens transparency, corneal epithelial repair, intraocular pressure (IOP) regulation, retinal signal transduction and retinal swelling following injury. The mouse phenotype findings implicate AQPs as potential drug targets for therapy of elevated IOP and ocular disorders involving the cornea, lens and retina. However, much research remains in defining cell-level mechanisms for the ocular AQP functions, in establishing the relevance to human eye disease of conclusions from knockout mice, and in developing AQP-modulating drugs. [Copyright &y& Elsevier]

Summary: Transgenic mice lacking renal aquaporins (AQPs), or containing mutated AQPs, have been useful in confirming anticipated AQP functions in renal physiology and in discovering new functions. Mice lacking AQPs 1-4 manifest defects in urinary concentrating ability to different extents. Mechanistic studies have confirmed the involvement of AQP1 in near-isosmolar fluid absorption in the proximal tubule, and in countercurrent multiplication and exchange mechanisms that produce medullary hypertonicity in the antidiuretic kidney. Deletion of AQPs 2-4 impairs urinary concentrating ability by reduction of transcellular water permeability in the collecting duct. Recently created transgenic mouse models of nephrogenic diabetes insipidus produced by AQP2 gene mutation offer exciting possibilities to test new drug therapies. Several unanticipated AQP functions in kidney have been discovered recently that are unrelated to their role in transcellular water transport. There is evidence for involvement of AQP1 in kidney cell migration after renal injury, of AQP7 in renal glycerol clearance, of AQP11 in prevention of renal cystic disease, and possibly of AQP3 in regulation of collecting duct cell proliferation. Future work in renal AQPs will focus on mechanisms responsible for these non–fluid-transporting functions, and on the development of small-molecule AQP inhibitors for use as aquaretic-type diuretics. [Copyright &y& Elsevier]

Abstract: Of the several aquaporin (AQP) water channels expressed in the central nervous system, AQP4 is an attractive target for drug discovery. AQP4 is expressed in astroglia, most strongly at the blood–brain and brain–cerebrospinal fluid barriers. Phenotype analysis of AQP4 knockout mice indicates the involvement of AQP4 in three distinct processes: brain water balance, astroglial cell migration and neural signal transduction. By slowing water uptake into the brain, AQP4 knockout mice manifest reduced brain swelling and improved outcome in models of cytotoxic cerebral oedema such as water intoxication, focal ischaemia and meningitis. However, by slowing the clearance of excess water from brain, AQP4 knockout mice do worse in models of vasogenic oedema such as brain tumour, abscess and hydrocephalus. AQP4 deficient astroglial cells show greatly impaired migration in response to chemotactic stimuli, reducing glial scar formation, by a mechanism that we propose involves AQP4-facilitated water flux in lamellipodia of migrating cells. AQP4 knockout mice also manifest increased seizure threshold and duration, by a mechanism that may involve slowed K+ uptake from the extracellular space (ECS) following neuroexcitation, as well as ECS expansion. Notwithstanding challenges in drug delivery to the central nervous system and their multiplicity of actions, AQP4 inhibitors have potential utility in reducing cytotoxic brain swelling, increasing seizure threshold and reducing glial scar formation; enhancers of AQP4 expression have potential utility in reducing vasogenic brain swelling. AQP4 modulators may thus offer new therapeutic options for stroke, tumour, infection, hydrocephalus, epilepsy and traumatic brain and spinal cord injury. [Copyright &y& Elsevier]

Abstract: Functional interaction of glial water channel aquaporin-4 (AQP4) and inwardly rectifying K+ channel Kir4.1 has been suggested from their apparent colocalization and biochemical interaction, and from the slowed glial cell K+ uptake in AQP4-deficient brain. Here, we report multiple lines of evidence against functionally significant AQP4–Kir4.1 interactions. Whole-cell patch-clamp of freshly isolated glial cells from brains of wild-type and AQP4 null mice showed no significant differences in membrane potential, barium-sensitive Kir4.1 K+ current or current–voltage curves. Single-channel patch-clamp showed no differences in Kir4.1 unitary conductance, voltage-dependent open probability or current–voltage relationship. Also, Kir4.1 protein expression and distribution were similar in wild-type and AQP4 null mouse brain and in the freshly isolated glial cells. Functional inhibition of Kir4.1 by barium or RNAi knock-down in primary glial cell cultures from mouse brain did not significantly alter AQP4 water permeability, as assayed by calcein fluorescence quenching following osmotic challenge. These studies provide direct evidence against functionally significant AQP4–Kir4.1 interactions in mouse glial cells, indicating the need to identify new mechanism(s) to account for altered seizure dynamics and extracellular space K+ buffering in AQP4 deficiency. [Copyright &y& Elsevier]

Abstract: Aquaporins (AQPs) are small, integral membrane proteins that facilitate water transport across cell membranes in response to osmotic gradients. Water transport across epithelia and endothelia in the peripheral lung and airways occurs during airway hydration, alveolar fluid transport and submucosal gland secretion. Several AQPs are expressed in the lung and airways: AQP1 in microvascular endothelia, AQP3 and AQP4 in airway epithelia, and AQP5 in type I alveolar epithelial cells, submucosal gland acini, and a subset of airway epithelial cells. Phenotype analysis of transgenic knockout mice lacking AQPs has defined their roles in the lung and airways. AQP1 and AQP5 provide the principal route for osmotically driven water transport between airspace and capillary compartments; however, alveolar fluid clearance in the neonatal and adult lung is not affected by their deletion, nor is lung fluid accumulation in experimental models of lung injury. In the airways, though AQP3 and AQP4 facilitate osmotic water transport, their deletion does not impair airway hydration, regulation of airway surface liquid, or fluid absorption. In contrast to these negative findings, AQP5 deletion in submucosal glands reduced fluid secretion by >50%. The substantially slower fluid transport in the lung compared to renal and secretory epithelia probably accounts for the lack of functional significance of AQPs in the lung and airways. Recent data outside of the lung implicating the involvement of AQPs in cell migration and proliferation suggests possible new roles for lung AQPs to be explored. [Copyright &y& Elsevier]

Background & Aims: Inhibitors of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel are predicted to prevent intestinal fluid secretion in cholera. We previously discovered low- affinity glycine hydrazide (GlyH) CFTR inhibitors that block CFTR at its external pore. The goal of this study was to develop potent CFTR inhibitors that are minimally absorbed and washed out of the intestinal lumen for application as antisecretory agents in cholera. Methods: GlyH analogs (malonic hydrazides, MalH) were chemically conjugated to various lectins (“MalH-lectin”) and purified. CFTR inhibition potency was measured by short-circuit current analysis, mechanism of action by patch-clamp, and antidiarrheal efficacy in closed-loop and suckling mouse models. Results: By lectin conjugation, we improved CFTR inhibitory potency by ∼100-fold (to 50 nmol/L) and retarded washout. High-affinity CFTR inhibition was abolished by MalH-lectin heat denaturation, protease digestion, or competition by mannose or unconjugated lectin. Patch-clamp analysis indicated CFTR inhibition by an external pore occlusion mechanism. Fluorescently labeled MalH-lectin remained membrane bound for >6 hours after washout, whereas washout occurred in a few minutes without the lectin. MalH-ConA and MalH-wheat (IC50 50–100 pmol) blocked cholera toxin-induced intestinal fluid secretion in closed intestinal loops in mice and greatly reduced mortality in a suckling mouse model of cholera. Conclusions: The high potency of MalH-lectin conjugates results from “anchoring” the CFTR-blocking MalH to cell surface carbohydrates by the lectin. The high-affinity, slow washout, and external site of action of the MalH-lectin conjugates support their further development as antisecretory drugs for enterotoxin-mediated secretory diarrheas. [Copyright &y& Elsevier]

Abstract: Aquaporin-1 (AQP1) inhibitors are predicted to have multiple clinical applications. Hg++ is a non-specific and toxic AQP1 blocker. We compared compounds with reported AQP1 inhibition activity, including DMSO, Au+++, Ag+, tetraethylammonium and acetazolamide. Water permeability was measured by stopped-flow light scattering in erythrocytes and volume marker dilution in epithelial cells. Au+++ inhibited AQP1 with IC50∼14μM, similar to 10μM for Hg++. DMSO slowed osmotic equilibration; however, the apparent inhibition was due to ‘osmotic clamp’ rather than AQP1 inhibition. Neither tetraethylammonium nor acetazolamide (to 10mM) inhibited AQP1. Our data indicate the need to identify new AQP1 inhibitors. [Copyright &y& Elsevier]

Abstract: Aquaporin-4 (AQP4) is expressed in astrocytes throughout the central nervous system, particularly at the blood–brain and brain–cerebrospinal fluid barriers. Phenotype analysis of transgenic mice lacking AQP4 has provided compelling evidence for involvement of AQP4 in cerebral water balance, astrocyte migration, and neural signal transduction. AQP4-null mice have reduced brain swelling and improved neurological outcome in models of (cellular) cytotoxic cerebral edema including water intoxication, focal cerebral ischemia, and bacterial meningitis. However, brain swelling and clinical outcome are worse in AQP4-null mice in models of vasogenic (fluid leak) edema including cortical freeze-injury, brain tumor, brain abscess and hydrocephalus, probably due to impaired AQP4-dependent brain water clearance. AQP4 deficiency or knock-down slows astrocyte migration in response to a chemotactic stimulus in vitro, and AQP4 deletion impairs glial scar progression following injury in vivo. AQP4-null mice also manifest reduced sound- and light-evoked potentials, and increased threshold and prolonged duration of induced seizures. Impaired K+ reuptake by astrocytes in AQP4 deficiency may account for the neural signal transduction phenotype. Based on these findings, we propose modulation of AQP4 expression or function as a novel therapeutic strategy for a variety of cerebral disorders including stroke, tumor, infection, hydrocephalus, epilepsy, and traumatic brain injury. [Copyright &y& Elsevier]

Abstract: We have developed an inducible mouse model of glaucoma based on episcleral vein cauterization (EVC). Intraocular pressure (IOP) elevation in adult mice was produced by cauterizing three episcleral veins. Serial IOP measurements were done by induction-impact tonometry. IOP was significantly elevated by 104±20% in 20 out of 23 mice (87%) within the first day after EVC, and remained elevated for 4 weeks, with mean IOP 94% higher in EVC-treated vs. contralateral control eyes. Aqueous outflow blockade was verified from the IOP response to pulsed fluid infusions into the anterior chamber. Retinal ganglion cell (RGC) loss, determined by retrograde labelling using Fluoro-Gold applied to the superior colliculous, was ∼20% at 2 weeks after EVC. We conclude that episcleral vein occlusion in mice produces significant and sustained elevation in IOP associated with increased outflow resistance and RGC loss, and thus may be useful to model glaucoma in genetically modified and drug-treated mice. [Copyright &y& Elsevier]

Transgenic mouse models of aquaporin (AQP) deletion and mutation have been instructive in elucidating the role of AQPs in renal physiology. Mice lacking AQP1 are unable to concentrate their urine because of low water permeability in the proximal tubule, thin descending limb of Henle, and outer medullary descending vasa recta, resulting in defective near-isosmolar fluid absorption in the proximal tubule and defective countercurrent multiplication. Mice lacking functional AQP2, AQP3, or AQP4 manifest various degrees of nephrogenic diabetes insipidus resulting from reduced collecting duct water permeability. Mice lacking AQP7 and AQP8 can concentrate their urine fully, although AQP7 null mice manifest an interesting defect in glycerol reabsorption. Two unexpected renal phenotypes of AQP null mice have been discovered recently, including defective proximal tubule cell migration in AQP1 deficiency, and cystic renal disease in AQP11 deficiency. AQPs thus are important in several aspects of the urinary concentrating mechanism and in functions unrelated to tubular fluid transport. The mouse phenotype data suggest the renal AQPs as targets for the development of aquaretics and potentially for therapy of cystic renal disease and acute renal injury. [ABSTRACT FROM AUTHOR]

Abstract: Gene transfer using non-viral vectors is a promising approach for the safe delivery of therapeutic DNA in genetic and acquired human diseases. Whereas the lack of specific immune response favors the use of plasmid–cationic polymer complexes, the limited efficacy and short duration of transgene expression impose major hurdles in the application of non-viral gene delivery techniques. Here, we review the major cellular, metabolic and physico-chemical impediments that non-viral vectors encounter before plasmid DNA enters the nucleus. Following endocytosis of DNA–polycation complexes, a large fraction of the DNA is targeted to the lysosomes. Since the cytosolic release of heterologous DNA is a prerequisite for nuclear translocation, entrapment and degradation of plasmid DNA in endo-lysosomes constitute one of the major impediments to efficient gene transfer. Plasmid DNA that escapes the endo-lysosomal compartment encounters the diffusional and metabolic barriers of the cytoplasm, reducing greatly the number of intact plasmids that reach the nucleosol. Nuclear translocation of DNA requires either the disassembly of the nuclear envelope or active nuclear transport via the nuclear pore complex. A better understanding of the cellular and molecular basis of non-viral vector trafficking from the extracellular compartment into the nucleus may provide strategies to overcome those obstacles that limit the efficiency of gene delivery. [Copyright &y& Elsevier]

Intestinal infection with Vibrio cholerae results in secretory diarrhea with potentially massive fluid losses and volume depletion. Morbidity and mortality associated with cholera remain a major problem in the developing world despite the success of oral rehydration therapy. New research aiming to inhibit cholera toxin binding to receptors in the intestine provides an attractive strategy for cholera therapy. Together with anti-secretory agents, including inhibitors of enkephalinase and of the cystic fibrosis transmembrane conductance regulator, new treatment options for managing severe diarrhea in cholera could soon be available. [Copyright &y& Elsevier]

Drug discovery and development is generally done in the commercial rather than the academic realm. Drug discovery involves target discovery and validation, lead identification by high-throughput screening, and lead optimization by medicinal chemistry. Follow-up preclinical evaluation includes analysis in animal models of compound efficacy and pharmacology (ADME: administration, distribution, metabolism, elimination) and studies of toxicology, specificity, and drug interactions. Notwithstanding the high-cost, labor-intensive, and non-hypothesis-driven aspects of drug discovery, the academic setting has a unique and expanding niche in this important area of investigation. For example, academic drug discovery can focus on targets of limited commercial value, such as third-world and rare diseases, and on the development of research reagents such as high-affinity inhibitors for pharmacological "gene knockout" in animal models ("chemical genetics"). This review describes the practical aspects of the preclinical drug discovery process for academic investigators. The discovery of small molecule inhibitors and activators of the cystic fibrosis transmembrane conductance regulator is presented as an example of an academic drug discovery program that has yielded new compounds for physiology research and clinical development. [ABSTRACT FROM AUTHOR]

A calcein fluorescence quenching method was applied to measure osmotic water permeability in highly differentiated primary cultures of brain astrocytes from wild-type and aquaporin-4 (AQP-4)-deficient mice. Cells grown on coverglasses were loaded with calcein for measurement of volume changes after osmotic challenge. Hypotonic shock producing twofold cell swelling resulted in a reversible ∼12% increase in calcein fluorescence, which was independent of cytosolic calcein concentration at levels well below where calcein self-quenching occurs. Calcein fluorescence was quenched in <200 ms in response to addition of cytosol in vitro, indicating that the fluorescence signal arises from changes in cytosol concentration. In astrocytes from wild-type CD1 mice, calcein fluorescence increased reversibly in response to hypotonic challenge with a half-time of 0.92 ± 0.05 s at 23°C, corresponding to an osmotic water permeability (P[sub f]) of ∼0.05 cm/s. P[sub f] was reduced 7.1-fold in astrocytes from AQP-4-deficient mice. Temperature dependence studies indicated an increased Arrhenius activation energy for water transport in AQP-4deficient astrocytes (11.3 ± 0.5 vs. 5.5 ± 0.4 kcal/mol). Our studies establish a calcein quenching method for measurement of cell membrane water permeability and indicate that AQP-4 provides the principal route for water transport in astrocytes. water transport; aquaporin-4; fluorescence quenching; brain swelling; cerebral edema. [ABSTRACT FROM AUTHOR]

Phenotype analysis has demonstrated that aquaporin-1 (AQP1) null mice are polyuric and manifest a urinary concentrating defect because of an inability to create a hypertonic medullary interstitium. We report here that deletion of AQP1 is also associated with a decrease in urinary pH from 6.15 ± (SE) 0.1 to 5.63 ± 0.07. To explore the mechanism of the decrease in urinary pH, we examined the expression of H[sup +]-ATPase in kidneys of AQP1 null mice. There was strong labeling for H[sup +]-ATPase in intercalated cells and proximal tubule cells in both AQP1 null and wild-type mice. Strong H[sup +]-ATPase immunostaining was also present in the apical plasma membrane of inner medullary collecting duct (IMCD) cells in AQP1 null mice, whereas no H[sup +]-ATPase labeling was observed in IMCD cells in wild-type mice. In addition, there was an increase in the prevalence of type A intercalated cells in the IMCD of AQP1 null mice, suggesting that the deletion of intercalated cells from the IMCD, which normally occurs during postnatal kidney development, was impaired. Western blot analysis of H[sup +]-ATPase expression in the different regions of the kidney demonstrated a significant increase in H[sup +]-ATPase protein in the inner medulla of AQP1 null mice compared with wild-type mice. There were no changes in H[sup +]-ATPase expression in the cortex or outer medulla. These results represent the first demonstration of apical H[sup +]-ATPase immunoreactivity in IMCD cells in vivo and suggest that the decrease in urinary pH observed in AQP1 null mice is due to upregulation of H[sup +]-ATPase in the IMCD. The induction of H[sup +]-ATPase expression in IMCD cells of AQP1 null mice may be related to the chronically low interstitial osmolality in these animals. The challenge will be to identify the molecular signal(s) responsible for the de novo H[sup +]-ATPase expression. [ABSTRACT FROM AUTHOR]

Activators of the CFTR Cl[sup -] channel may be useful for therapy of cystic fibrosis. Short-circuit current (I[sub sc]) measurements were done on human bronchial epithelial cells to characterize the best flavone and benzimidazolone CFTR activators identified by lead-based combinatorial synthesis and high-throughput screening. The 7,8-benzoflavone UC[sub CF]-029 was a potent activator of Cl[sup -] transport, with activating potency (<1 µM) being much better than other flavones, such as apigenin. The benzimidazolone UCCF-853 gave similar I[sub sc] but with lower potency (5-20 µM). In combination, the effect induced by maximal UCCF-029 and UCCF-853 was 50-80% greater than that of either compound alone. The apparent activating potencies (K[sub d]) of UCCF-029, UCCF-853, and apigenin increased strongly with increasing basal CFTR activity: for example, K[sub d] for activation by UCCF029 decreased from >5 to <0.4 µM with increasing basal I[sub sc] from ∼4 µA/cm² to ∼12 µA/cm². This dependence was confirmed in permeabilized Fischer rat thyroid cells stably expressing CFTR. Our results demonstrate efficacy of novel CFTR activators in bronchial epithelia and provide evidence that activating potency depends on basal CFTR activity. [ABSTRACT FROM AUTHOR]

Mice deficient in the epidermal water/glycerol transporter aquaporin-3 (AQP3) have reduced stratum corneum (SC) hydration and skin elasticity, and impaired barrier recovery after SC removal. SC glycerol content is reduced 3-fold in AQP3 null mice, whereas SC structure, protein/lipid composition, and ion/osmolyte content are not changed. We show here that glycerol replacement corrects each of the defects in AQP3 null mice. SC water content, measured by skin conductance and ³H[sub 2]O accumulation, was 3-fold lower in AQP3 null vs. wild-type mice, but became similar after topical or systemic administration of glycerol in quantities that normalized SC glycerol content. SC water content was not corrected by glycerol-like osmolytes such as xylitol, erythritol, and propanediol. Orally administered glycerol fully corrected the reduced skin elasticity in AQP3 null mice as measured by the kinetics of skin displacement after suction, and the delayed barrier recovery as measured by transepidermal water loss after tape-stripping. Analysis of [[sup 14]C]glycerol kinetics indicated reduced blood-to-SC transport of glycerol in AQP3 null mice, resulting in slowed lipid biosynthesis. These data provide functional evidence for a physiological role of glycerol transport by an aquaglyceroporin, and indicate that glycerol is a major determinant of SC water retention, and mechanical and biosynthetic functions. Our findings establish a scientific basis for the >200-yr-old empirical practice of including glycerol in cosmetic and medicinal skin formulations. [ABSTRACT FROM AUTHOR]

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) protein, an epithelial chloride channel expressed in the airways, pancreas, testis, and other tissues. A central question is how defective CFTR function in CF leads to chronic lung infection and deterioration of lung function. Several mechanisms have been proposed to explain lung disease in CF, including abnormal airway surface liquid (ASL) properties, defective airway submucosal gland function, altered inflammatory response, defective organellar acidification, loss of CFTR regulation of plasma membrane ion transporters, and others. This review focuses on the physiology of the ASL and submucosal glands with regard to their proposed role in CF lung disease. Experimental evidence for defective ASL properties and gland function in CF is reviewed, and deficiencies in understanding ASL/gland physiology are identified as areas for further investigation. New model systems and measurement technologies are being developed to make progress in establishing lung disease mechanisms in CF, which should facilitate mechanism-based design of therapies for CF. [ABSTRACT FROM AUTHOR]

Describes a pleural surface fluorescence method to measure Na[sup +] and Cl[sup -] transport in perfused mouse lungs. Filling of air space with aqueous fluid containing membrane-impairment fluorescent indicators of Cl[sup -] or Na[sup +]; Instillation of a Cl[sup -]-free solution into the air space; Evidence for cAMP-stimulated transcellular Cl[sup -] and Na[sup +] transport.

Examines the submucosal gland secretions in airways from cystic fibrosis patients. Measurement of sodium ion and hydrogen ion concentration; Application of fluorescence method for the measurement of ionic composition; Contribution of elevated gland fluid viscosity in promoting bacterial colonization in airway.

Examines the lack of aquaporin-1 water channels in the processing of dietary fat in transgenic mice. Employment of immunocytochemistry in detecting the presence of aquaporin-1; Factors leading to dietary fat processing abnormality.

Analyses organ cell physiology in transgenic mice. General considerations in phenotype comparisons; Principal parameters describing cardiovascular physiology; Urinary concentrating ability in mice deficient in aquaporin water channel proteins.

Examines luminal hypotonicity in proximal renal tubules of aquaporin-1 knockout mice. Osmolality in plasma and late proximal tubular fluid in Aquaporin knockout and wild-type mice; Significant reduction in luminal tonicity compared with plasma in wild-type mice; Possibility that osmotic water permeability can be reduced in proximal kidney tubules.

Focuses on the role of membrane water-transporting proteins, the aquaporins, in high lung water permeability and lung physiology. Barriers to water transport in lung; Water permeabilities in lung; Aquaporin water channels in the lung; Functional analysis of aquaporin knockout mice.

Summarizes progress in water-transporting mechanisms across cell membranes. Water transport biophysics; Characteristics of water-transporting proteins; Systems for expression of water channel properties.

Investigates the mercurial insensitivity and key residues involved in mercurial-insensitive water channel (MIWC), small integral membrane proteins which have homology to the major intrinsic protein of lens fiber. Mutation of amino acids just proximal to the conserved NPA motifs; Site-directed mutagenesis; Immunofluorescence; cRNA transcription.

Examines the nature and tissue distribution of urea transporters in the kidney. Isolation of mRNA from different tissues and expression in Xenopus oocytes; Urea and methylglucose uptake; Existence of a urea transporting pathway in liver; Difference between cAMP-dependent urea transport in the renal medulla and in erythrocyte or liver; Lack of involvement of vesicular trafficking.

Characterizes the water permeability reduction in the inner medullary collecting duct (IMCD) of aquaporin-4 (AQP4) knockout mice. Description of the AQP4 knockout mice; Additive water permeabilities in the joint expression of AQP3 and AQP4; Function of the AQP4 for majority of the basolateral membrane water movement in IMCD.

Presents a study on the role of aquaporin-1 (AQP1) in proximal tubule water transport and fluid reabsorption in mice. Methodology used in the study; Measurement of transepithelial osmotic water permeability and fluid reabsorption under in vitro conditions; Major pathway for osmotically driven water transport; Conclusion on additional aquaporin-type water channels.

Tests whether osmotic water permeability (Pf)type I alveolar epithelial cells is high enough to account for the high Pf of he intact lung. Measurements of water permeability between the airspace and vasulature in rat lung by a pleural surface fluorescence method; Development of a improved method of isolating type I cells based on immunoselection.