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PubMed1989

Effects of serosal anion composition on the permeability properties of rabbit urinary bladder.

This study describes the effects of serosal Cl- and HCO3- substitution on transepithelial Na+ transport and basolateral membrane properties of the rabbit urinary bladder. Replacement of Cl- with NO3-, SCN-, and Br- had no effect on transepithelial Na+ transport or the basolateral membrane potential (Vbl). However, gluconate, isethionate, and cyclamate (anions that were shown previously to be not as permeable as Cl- through the basolateral membrane anion channel), decreased transepithelial Na+ transport and depolarized Vbl. Replacement of HCO3- also produced a decrease in transepithelial Na+ transport and a depolarization of Vbl. Utilizing conventional and K+-specific microelectrodes, we found the depolarization to be due to a reduction in basolateral K+ conductance. This depolarization was reversible only when Cl- was returned to the serosal solution, the normally permeant anion NO3- being unable to affect repolarization, suggesting that both the K+ and Cl- conductance are reduced during depolarization. A lag period of some 4 min preceded the repolarization of Vbl. The Na+-H+ exchange blocker amiloride prolonged the lag phase associated with repolarization, whereas niflumic acid, a Cl-(-)HCO3- exchange blocker (in red blood cells) reduced the magnitude of Vbl repolarization. Because of the possible involvement of the exchangers it is believed that the lag phase represents a volume-dependent and/or pH-dependent reactivation of the basolateral membrane conductances.

Amiloride↗
PubMed2003

Bilateral microsporidial keratoconjunctivitis in an immunocompetent non-contact lens wearer.

PURPOSE: To describe an immunocompetent male with bilateral microsporidial keratoconjunctivitis who responded to treatment with albendazole, propamidine, and fumagillin. METHODS: Corneal and conjunctival epithelial scrapings from a man with bilateral keratoconjunctivitis previously treated with topical corticosteroids were evaluated by Gram stain and by fluorescence microscopy. RESULTS: Gram stain and fluorescence microscopy of corneal epithelial scraping revealed organisms characteristic of microsporidia. Results of human immunodeficiency virus antibody testing were reported as nonreactive. Symptoms of ocular discomfort and clinical signs of keratoconjunctivitis resolved after five weeks of treatment that included systemic albendazole and topical propamidine isethionate 0.1% and fumagillin bicyclohexylammonium salt. A follow-up conjunctival scraping failed to detect any residual organisms 2 weeks after cessation of all treatment. CONCLUSION: Microsporidial ocular infection occurred in an immunocompetent non-contact lens wearer. Microsporidial keratoconjunctivitis should be considered in any individual with atypical multifocal diffuse epithelial keratitis, regardless of immune status or recent history of contact lens wear.

Adult↗
PubMed1972

Oxidative phosphorylation. The effect of anions on the inhibition by triethyltin of various mitochondrial functions, and the relationship between this inhibition and binding of triethyltin.

1. The binding of triethyltin to rat liver mitochondria is unaffected by the nature of the predominant anion in the incubation medium. 2. With chloride, bromide or iodide as the predominant anion, ATP synthesis linked to the oxidation of pyruvate or succinate and ATP hydrolysis stimulated by 2,4-dinitrophenol are much more sensitive to triethyltin than they are when nitrate or isethionate is the predominant anion. 3. When nitrate or isethionate is the predominant anion, oxygen uptake stimulated by 2,4-dinitrophenol is not inhibited by triethyltin. 4. In the presence of nitrate or isethionate anions, inhibition of ATP synthesis is directly related to the binding of triethyltin to mitochondria. 5. The relationship of the above effects to the anion-hydroxide ion exchange mediated by triethyltin and the relevance of this to published arrangements for coupling of electron transport to ATP synthesis are discussed.

Adenosine Triphosphate↗
PubMed1968

The ionic content of mammalian non-myelinated nerve fibres and its alteration as a result of electrical activity.

1. A study has been made of the ionic content, and of the fibre water, of rabbit desheathed vagus nerves at rest and after activity in various modified Locke solutions.2. In normal Locke solution the intracellular sodium amounted to 86.1 mumole/g dry, and the intracellular potassium 186.0 mumole/g dry. Since the fibre water amounted to 1.124 g/g dry the intracellular sodium and potassium concentrations were 76.6 and 165.5 m-mole/kg fibre water, respectively.3. In potassium-free Locke solution the intracellular sodium and potassium concentrations were 111.0 and 121.7 m-mole/kg, respectively. The intracellular chloride concentration was 40.5 m-mole/kg.4. In normal Locke solution, a brief period of stimulation followed by a 10 min recovery period produced no significant change in the intracellular contents of potassium, sodium, or water.5. However, in chloride-Locke solution from which the potassium had been omitted, or to which ouabain (1 mM) had been added, stimulation caused a loss of potassium per impulse of about 20 p-mole/mg dry, i.e. about 4 p-mole/mg wet. A similar loss was found in isethionate-Locke solution that was potassium-free. There was no significant change in any of the other quantities measured (sodium, chloride, and fibre water).6. The efflux of radioactively labelled potassium was measured in potassium-free Locke solution at rest (k(r)) and during activity (k(s)). At 24 degrees C, k(r) was 0.0084 min(-1) and k(s) was 0.000178 impulse(-1).7. When the chloride of Locke solution was replaced by isethionate there was an increase in both k(r) (about 12%) and k(s) (about 21%).8. Ouabain (1 mM) increased k(s) (by about 70%). This increase seemed to be independent of whether the anion present was chloride or isethionate.9. It is argued that these results indicate that the electrogenicity of the pump plays a relatively small role in maintaining the ionic balance in mammalina C fibres.

Amidines↗
PubMed1994

Comparative aspects of utilization of sulfonate and other sulfur sources by Escherichia coli K12.

Selected biochemical features of sulfonate assimilation in Escherichia coli K-12 were studied in detail. Competition between sulfonate-sulfur and sulfur sources with different oxidation states, such as cysteine, sulfite and sulfate, was examined. The ability of the enzyme sulfite reductase to attack the C-S linkage of sulfonates was directly examined. Intact cells formed sulfite from sulfonate-sulfur. In cysteine-grown cells, when cysteine was present with either cysteate or sulfate, assimilation of both of the more oxidized sulfur sources was substantially inhibited. In contrast, none of three sulfonates had a competitive effect on sulfate assimilation. In studies of competition between different sulfonates, the presence of taurine resulted in a decrease in cysteate uptake by one-half, while in the presence of isethionate, cysteate uptake was almost completely inhibited. In sulfite-grown cells, sulfonates had no competitive effect on sulfite utilization. An E. coli mutant lacking sulfite reductase and unable to utilize isethionate as the sole source of sulfur formed significant amounts of sulfite from isethionate. In cell extracts, sulfite reductase itself did not utilize sulfonate-sulfur as an electron acceptor. These findings indicate that sulfonate utilization may share some intermediates (e.g., sulfite) and regulatory features (repression by cysteine) of the assimilatory sulfate reductive pathway, but sulfonates do not exert regulatory effects on sulfate utilization. Other results suggest that unrecognized aspects of sulfonate metabolism, such as specific transport mechanisms for sulfonates and different regulatory features, may exist.

Cysteine↗
PubMed1984

Essential role of sodium and chloride for theophylline-induced choleresis in the isolated perfused rat liver.

Active secretion of electrolytes by hepatocytes is believed to be responsible for bile acid-independent canalicular bile flow (BAICF). Theophylline, which enhances BAICF, has been shown to enhance electrogenic Cl- secretion in a number of other epithelia. Such transport is dependent on Na+ and Cl-. Thus, the mechanism of theophylline choleresis may also involve stimulation of electrogenic Cl- secretion of the liver. This hypothesis was tested by studying the effect of ion substitution on theophylline choleresis in isolated perfused rat livers. Addition of theophylline (0.1 mmol) and dibutyryl cAMP (0.05 mmol) to 100 ml perfusate, in a single dose, increased bile flow and biliary secretion of Na+ and Cl- reversibly. These effects of theophylline were virtually abolished when perfusate Na+ (146 mM) was replaced by Li+ (146 mM) or choline+ (120 mM), and when Cl- (127 mM) was replaced by 120 mM NO-3, acetate- or isethionate-. Since even the permeable ions like Li+ and NO-3 could not substitute for Na+ and Cl-, these results show that the effect of theophylline on BAICF is specifically dependent on the presence of Na+ and Cl- in the perfusate. We propose, by analogy to other epithelia, that an electrogenic Cl- secretion mechanism is present in the liver. Theophylline, acting via cAMP, stimulates this transport process, thereby enhancing BAICF.

Animals↗
PubMed1987

Ion dependence of neurotransmitter uptake: inhibitory effects of ion substitutes.

Several ions commonly used as substitutes for Na+ or Cl- were found to inhibit directly the high-affinity uptake of norepinephrine, dopamine, serotonin, and gamma-aminobutyric acid, but not glutamate or glutamine. When Na+ was partially replaced by any of several different cations or sucrose the uptake of all neurotransmitters studied except that of serotonin was reduced more than could be accounted for by just the inhibitory effect of the cation substitute. In contrast, when Cl- was partially replaced by any of several anions only the uptake of dopamine was reduced more than could be accounted for by the inhibitory effect of the anion substitute. These results suggest that for most neurotransmitters the electrochemical potential for Na+, but not for Cl-, contributes to the uptake driving force. When either Na+ or Cl- was totally replaced by an ion substitute or by sucrose the high-affinity uptake was virtually abolished, an exception being that glutamate uptake was not affected when isethionate was substituted for Cl-. The lack of uptake in the absence of either Na+ or Cl- may reflect a specific role for these ions in either increasing the affinity between the substrate and the carrier, or facilitating the translocation process. Alternatively, the transport carriers may undergo a nonspecific conformational change to an inactive form in the absence of Na+ or Cl-. A partial substitution of Na+ with Li+ or sucrose differentially affected the kinetics of uptake in that replacement with Li+, but not sucrose, usually resulted in a marked increase in the Km values.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Macrolide compounds, ivermectin and milbemycin D, stimulate chloride channels sensitive to GABAergic drugs in cultured chick spinal neurons.

1. The effects of ivermectin (IVM) and milbemycin D (MMD) on cultured embryonic spinal neurons were investigated, using the whole-cell recording technique. 2. IVM and MMD caused Cl- current under voltage-clamp conditions. 3. The reversal potential of the MMD-evoked Cl- current was shifted in a positive direction when half of the external Cl- was substituted by isethionate. 4. The MMD-evoked current was inhibited by picrotoxinin and bicuculline, whereas it was enhanced by diazepam. 5. Different characteristics of desensitization were observed between the MMD- (IVM-) and muscimol-induced effects. 6. These results suggest that IVM and MMD directly activate the Cl- channel through their specific sites modulated by GABAergic drugs.

Animals↗
PubMed1979

Electrolyte secretion by the isolated cat pancreas during replacement of extracellular bicarbonate by organic anions and chloride by inorganic anions.

1. The effect of replacing extracellular bicarbonate and chloride by other anions on the volume and composition of secretin-stimulated pancreatic juice has been analysed in the isolated, perfused cat pancreas. 2. The anions of some aliphatic carboxylic acids were able partially to substitute for bicarbonate in sustaining pancreatic secretion. The order of effectiveness was: acetate greater than proprionate greater than butyrate greater than formate. 3. The rate of secretion in the presence of 25 mM-acetate was 42% of that achieved with 25 mM-bicarbonate. The concentration of acetate in the secretion varied with flow rate, reaching a maximum of 120 mM at high flow rates and declining at lower flow rates, with reciprocal changes in chloride concentration. Bicarbonate was always present in the secretion at a concentration of 5--7 mM. 4. Inorganic anions were able totally or partially to substitute for chloride in sustaining secretion. In relation to chloride, their degree of effectiveness was: chloride = bromide = or greater than nitrate greater than iodide greater than sulphate greater than methyl sulphate greater than isethionate. Those anions which had no effect on secretion rate (i.e. bromide and nitrate) also had no effect on the bicarbonate concentration of the secretion and themselves appeared in the secretion in place of chloride. Those anions which inhibited secretion increased the bicarbonate concentration in the secretion in proportion to the degree of inhibition they caused (i.e. the increase was greatest with isethionate). 5. When perfusate chloride was only partially replaced by bromide or iodide the ratios of chloride: bromide and chloride: iodide in the secretion were approximately equal to those in the perfusate. 6. The carbonic anhydrase inhibitor acetazolamide reduced secretory rate and bicarbonate concentration when added to normal perfusion fluid or chloride-substituted fluids, but had no effect following replacement of perfusate bicarbonate by acetate. 7. These observations illustrate that an extracellular source of permeant anions is required for optimal pancreatic bicarbonate secretion to occur. This may indicate the participation of an anion exchange carrier in the transport events responsible for this secretory process.

Acetazolamide↗
PubMed1999

Anaerobic oxidations of cysteate: degradation via L-cysteate:2-oxoglutarate aminotransferase in Paracoccus pantotrophus.

Anoxic, fresh-water enrichment cultures to oxidize different organosulfonates were set up with nitrate, ferric iron or sulfate as electron acceptors. Pure cultures were easily obtained with two naturally occurring sulfonates, cysteate (2-amino-3-sulfopropionate) and taurine (2-aminoethanesulfonate), under nitrate-reducing conditions. These two sulfonates were also oxidized during reduction of iron(III), though isolation of pure cultures was not successful. One nitrate-reducing cysteate-oxidizing bacterium, strain NKNCYSA, was studied in detail. It was identified as Paracoccus pantotrophus. Eighteen sulfonates were tested, and the organism degraded cysteate, taurine, isethionate (2-hydroxyethanesulfonate), sulfoacetate or 3-aminopropanesulfonate with concomitant reduction of nitrate, presumably to molecular nitrogen. The carbon skeleton of these substrates was converted to cell material and, presumably, CO2. The amino group was released as ammonia and the sulfono moiety was recovered as sulfate. Cell-free extracts of P. pantotrophus NKNCYSA contained constitutive L-cysteate:2-oxoglutarate aminotransferase (EC 2.6.1.-) and glutamate dehydrogenase (EC 1.4.1.4). Taurine:pyruvate aminotransferase, in contrast, was inducible.

Anaerobiosis↗
PubMed1972

Conductance change during the inhibitory potential in the guinea-pig taenia coli.

1. Effects of membrane polarization and of reduction in external K and Cl concentration on the inhibitory potential were investigated in the guinea-pig taenia coli.2. Depolarization of the membrane increased the inhibitory potential while hyperpolarization decreased it. The relationship between the degree of membrane polarization and the amplitude of inhibitory potential was linear. The inhibitory potential was abolished or slightly reversed in polarity, when the membrane was hyperpolarized by 25-40 mV in different preparations.3. Removal of external K ion depolarized the membrane for about 5 min and increased the inhibitory potential more than could be accounted for by the depolarization. Readmission of K transiently hyperpolarized the membrane, probably due to an activation of the Na-K pump, and reduced the inhibitory potential, but no reversal of polarity in the inhibitory potential was observed during this hyperpolarizing phase.4. The membrane was transiently depolarized when the external Cl concentration was reduced by substituting with isethionate. Hyperpolarization was produced by restoring the external Cl concentration to normal. Changes in the amplitude of inhibitory potentials during alterations in Cl concentration occurred as expected from the shift of the membrane potential.5. From the results, it is concluded that the membrane conductance is increased during the inhibitory potential, and that an increase in the K permeability is the main factor for hyperpolarization of the membrane.

Action Potentials↗
PubMed1995

Comparison of transport properties of the reduced folate carrier and folate receptor in murine L1210 leukemia cells.

This laboratory previously described an L1210 murine leukemia cell line with a functional defect in the reduced folate carrier and increased expression of folate receptor-beta (F2-MTXrA). This cell line was used to characterize methotrexate (MTX) influx mediated by folate receptor-beta and to compare this with influx mediated by the reduced folate carrier in L1210 parental cells. Influx of 0.2 microM MTX in F2-MTXrA cells was one-third that of L1210 cells and was abolished by very low concentrations of folic acid. Kinetic analysis revealed that MTX transport mediated by folate receptor-beta exhibited an influx kappa t one-third, and an influx Vmax one-fourth, that of the reduced folate carrier. Metabolic inhibitors markedly suppressed influx in F2-MTXrA cells but had no effect on MTX influx in L1210 cells. MTX influx in both cell lines was inhibited by the organic anions probenecid, sulfobromophthalein, and CI-920, but to a lesser extent in F2-MTXrA cells. The inhibitory effects of these anions on transport in F2-MTXrA cells could be attributed to their inhibition of MTX binding to the folate receptor. Although MTX influx in both cell lines was not sodium dependent, removal of extracellular chloride increased influx 2-fold in L1210 cells while markedly inhibiting influx in F2-MTXrA cells. Substitution of Cl- with isethionate or NO3- partially restored influx in the latter cells, whereas SO4(2-) was inhibitory. Anions enhanced MTX binding to folate receptor-beta with isethionate > SO4(2-) > Cl-. Decreasing the buffer pH to 6.2 produced a 69% reduction, and a 260% increase, in MTX influx in L1210 cells and F2-MTXrA cells, respectively. The data indicate that folate receptor-beta-mediated MTX influx has properties fundamentally different from transport mediated by the reduced folate carrier in terms of energy, ion, and pH dependence. There was no evidence indicating that these processes are functionally linked.

Animals↗
PubMed1987

A chloride-bicarbonate exchanging anion carrier in vascular smooth muscle of the rabbit.

Cl- efflux into various incubation media (PSS) was studied in pieces of rabbit aortae loaded with 36Cl. Replacement of HCO3-/CO2 by HEPES/O2 in the PSS increased the rate of Cl- efflux by a factor of 2.4. This effect was suppressed in Cl(-)-free PSS containing isethionate, propionate, or benzenesulfonate, but not in NO3(-)-PSS, or Br(-)-PSS. The stimulant effect of HCO3- withdrawal on Cl-efflux was reduced by 140 microM DIDS, but not by 1 mM furosemide. The Cl- efflux was temperature-dependent (Q10 = 2.3-2.5), and it was not affected on depolarisation by high [K+]o. The [Cl-]i of rabbit aorta determined by uptake studies with 36Cl, decreased slightly (by 15%) below controls in PSS containing 140 microM DIDS, but drastically (from 32.6 to 13.5 mM, i.e. by 59%) in PSS containing 1 mM furosemide. Withdrawal of HCO3-/CO2 depolarized rabbit pulmonary artery in standard PSS and in Br(-)-PSS or NO3(-)-PSS, but not in benzenesulfonate-PSS. The pHi of rabbit aorta determined by the distribution of (14C)-DMO, increased in Cl(-)-free PSS containing isethionate or glucuronate. It is concluded that transport mechanisms play a major role in the distribution of Cl- in vascular smooth muscle, and that a membrane anion carrier operates in this tissue which can transport Cl- and HCO3- across the cell membrane. This mechanism seems to be involved in the regulation of pHi. However, the known high [Cl-]i of vascular smooth muscle is rather mediated by the furosemide-sensitive Na-K-Cl cotransport than by this anion carrier.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1987

Activity of lipid-soluble inhibitors of dihydrofolate reductase against Pneumocystis carinii in culture and in a rat model of infection.

Trimetrexate and BW301U (piritrexim isethionate), lipid-soluble inhibitors of dihydrofolate reductase, are potent inhibitors of the growth of Pneumocystis carinii in culture with WI-38 cells. Inhibition was observed with 0.1 microgram of trimetrexate or BW301U per ml. Trimethoprim is ineffective at 100 micrograms/ml in this culture system. Both trimetrexate and BW301U were effective as prophylactic agents against P. carinii pneumonia in rats; trimetrexate at 7.5 mg/kg protected 9 of 10 rats, and BW301U at 5 mg/kg protected 4 of 10.

Animals↗
PubMed1997

Haemonchus contortus: cloning and functional expression of a cDNA encoding ornithine decarboxylase and development of a screen for inhibitors.

Polyamines (PA) are essential for viability and replication of all cells; organisms either synthesize PA or acquire them from the environment. How nematodes that parasitize the gut satisfy their PA requirement has not been resolved. The primary regulatory enzyme in PA biosynthesis in most animals is ornithine decarboxylase (ODC). This enzyme has recently been characterized in free-living nematodes and in the parasitic species. Haemonchus contortus. Nematode and mammalian ODC are reported to differ in subcellular localization, kinetics, and sensitivity to inhibitors. We cloned an H. contortus cDNA that encodes a full-length ODC (sequence data from this article have been deposited with the GenBank Data Library under Accession Nos. AF016538 and AF016891). This cDNA was functionally expressed in strains of Escherichia coli and Saccharomyces cerevisiae that lack ODC and are dependent upon exogenous PA for survival. Expression of nematode ODC reversed the PA-dependence phenotype of both microorganisms. The complemented yeast strain was used to develop a nutrient-dependent viability screen for selective inhibitors of nematode ODC. The antiprotozoal drug stilbamidine isethionate was identified as active in this screen, but biochemical characterization revealed that this compound did not inhibit ODC. Instead, like other cationic diamidines, stilbamidine probably inhibits yeast S-adenosylmethionine decarboxylase. Nonetheless, the activity in the screen of the known ODC inhibitor difluoromethylornithine (DFMO) validates the concept that specific recombinant microorganisms can serve as the basis for extremely selective and facile screens.

Amino Acid Sequence↗
PubMed1999

Effects of inhibitors and substitutes for chloride in lumen on p-aminohippurate transport by isolated perfused rabbit renal proximal tubules.

The transport step for p-aminohippurate (PAH) from cell to lumen across the luminal membrane of rabbit proximal tubules has not been adequately defined. To examine this process more closely, we determined the effects of possible transport inhibitors and substitutes for chloride on PAH secretion in isolated perfused S2 segments of rabbit proximal tubules. The addition of 4-acetamido-4'-isothiocyano-2,2' disulfonic stilbene (10(-4) M) to the perfusate irreversibly inhibited PAH secretion, whereas the addition of probenecid (10(-4) M) to the perfusate reversibly inhibited PAH secretion. PAH secretion was unaffected by thiocyanate replacement of chloride in the luminal perfusate, reversibly inhibited by 15 to 20% by methyl sulfate replacement, and irreversibly inhibited by isethionate replacement. Because the luminal membrane is at least as permeable to thiocyanate as to chloride, less permeable to methyl sulfate, and much less permeable to isethionate, these data suggest that the PAH transport step from cells to lumen does not require chloride in the lumen but does require a highly permeant anion. During inhibition of PAH transport from cells to lumen, PAH uptake across the basolateral membrane was also reduced, suggesting some type of feedback inhibition. The data are compatible with PAH transport across the luminal membrane by an anion exchanger, a potential-driven uniporter, both carriers, or a carrier that can function in both modes.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1994

Capillary zone electrophoresis assay of the uridine diphosphate N-acetylmuramyl peptide precursors and the disaccharide pentapeptide derivative of bacterial cell wall peptidoglycan.

Uridine diphosphate N-acetylmuramyl peptide (EDP-MurNac) precursors and disaccharide pentapeptide of bacterial cell wall peptidoglycan were extracted from Enterobacter colacae cells and examined by capillary zone electrophoresis. Five UDP-MurNac derivatives with dibromopropamidine isethionate as the internal standard, and disaccharide pentapeptide with pyrimethamine as the internal standard, were successfully and rapidly analysed by using a fused-silica capillary and sodium phosphate buffer in methanol as the organic modifier at appropriate pH. Accurate quantitation was also achieved. The method provides the potential to investigate quantitatively the effect of antibacterials on the biosynthesis of peptidoglycan and to determine the relative cellular concentrations of the murein precursors within the cell cycle.

Cell Cycle↗
PubMed1991

Novel chloride conductance in the membrane of bovine chromaffin cells activated by intracellular GTP gamma S.

1. The effects of introducing the non-hydrolysable GTP analogue guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) into perfused bovine chromaffin cells were studied by a combination of the tight-seal whole-cell patch-clamp technique and Fura-2 fluorescence [Ca2+]i measurements. 2. GTP gamma S (5-300 microM) induced a slowly developing transient current (inwardly directed at the holding potential -60 to -70 mV) and [Ca2+]i oscillations. The current activated with a 10-50 s delay after the start of whole-cell dialysis, peaked at 70-120 s and decayed almost to its initial level during the next 150-300 s. Calcium oscillations were observed within the first 100-150 s of cell perfusion. 3. GTP competitively lowered the probability of current activation by GTP gamma S. At low GTP gamma S/GTP ratio (5 and 300 microM, respectively) activation of the current was observed only rarely. 4. The activation of the current was accompanied by an increase in conductance but not by changes in the current reversal potential. The changes in the conductance did not depend on the membrane potential; no time-dependent relaxation of the current was induced by steps in the membrane voltage. 5. The current reversal potential was close to the Cl- equilibrium potential; changes in the extracellular Cl- concentration induced corresponding changes in the current amplitude and shifted its reversal potential. The permeability to larger anions--aspartate, glutamate and isethionate--was about one-tenth of that for chloride. 6. Single-channel conductance, estimated from the ratio of the mean current and its variance, was about 1-2 pS. 7. The current could be reversibly blocked by 4,4'-diisothiocyanatostilbene-2,2'-disulphonate (DIDS, 10 microM), chlorpromazine (5 microM) and tolbutamide (0.5-5 mM). 8. It is suggested that the GTP gamma S-induced increase in the permeability to Cl- ions is due to a G protein-mediated production of an as yet unidentified second messenger.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗