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R Greger

Publications and source records attributed to R Greger.

At least 19 recordsLinked to original sources
PubMed1992

Small-conductance chloride channels induced by cAMP, Ca2+, and hypotonicity in HT29 cells: ion selectivity, additivity and stilbene sensitivity.

Previous studies in HT29 cells utilizing the cell-attached nystatin (CAN) method [Greger R, Kunzelmann K (1991) Pflügers Arch 419:209-211] have revealed that the Cl- channels induced by cAMP or by increasing cytosolic Ca2+, e.g. by addition of ATP, and by hypotonic cell swelling share in common their conductance, which was so small in our studies [Kunzelmann et al. (1992) Pflügers Arch (in press)] that we could not resolve it at the single-channel level. This prompted the question whether these Cl- conductances can be distinguished in terms of their ion selectivity and sensitivity towards inhibitors. Whether these pathways are additive or not was also examined. The present study utilized the whole-cell patch-clamp and the CAN methods. A total of 160 patches were studied. In whole-cell patches 8-(4-chlorophenylthio)-cAMP (cAMP, 0.1 +/- 1 mmol/l) induced a significant depolarization by 5 mV and a twofold increase in conductance (G) from 6.2 +/- 1.5 nS to 11.7 +/- 3.2 nS (n = 15). Total replacement of Cl- by Br- and I- in cAMP-treated cells hyperpolarized the membrane voltage (V) significantly from -35 +/- 2.8 to -39 +/- 3.4 and -45 +/- 3.3 mV respectively, but had no detectable effect on G, which was 11.9 +/- 3.3 nS in the case of Br- and 11.8 +/- 3.3 nS in the case of I-. Hence, the permselectivity of the cAMP pathway was I- > Br- > Cl-, but the conductances for these anions were all indistinguishable.(ABSTRACT TRUNCATED AT 250 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

Ion conductances of isolated cortical collecting duct cells.

The study of ion conductances in the intact cortical collecting duct (CCD) with the patch-clamp method is rather difficult. An optimized method to isolate CCD cells from rat kidneys using an in vivo followed by an in vitro enzyme digestion is described. Individual CCD segments were collected after this digestion and incubated in EGTA-buffered medium. This procedure resulted in single cells or cell clusters. These freshly isolated CCD cells were studied with different modifications of the patch-clamp method. Membrane voltages measured in the cell-attached-nystatin configuration were -74 +/- 1 mV (n = 13) and -68 +/- 3 mV (n = 22) in cells isolated from normal and mineralocorticoid-treated rats respectively. These values and those measured with the nystatin-perforated slow-whole-cell configuration (-79 +/- 1 mV, n = 23) are comparable to those measured in principal cells of isolated CCD segments. The cells hyperpolarized after the addition of amiloride and depolarized with the addition of adiuretin to the bath. The amiloride effect was enhanced when cells were isolated from deoxycorticosterone-acetate-treated rats. The cells were strongly depolarized upon elevation of the extracellular K(+)-concentration and did not demonstrate a measurable Cl- conductance. A large-conductance K+ channel (174 pS, n = 5, cell-attached, 145 mmol/l K+ in the pipette; 140 pS, n = 12, cell-free, 3.6 mmol/l K+ in the bath) was seen. It had a very low activity on the cell, but a high open probability when excised into a solution with 1 mmol/l Ca2+ on the cytosolic side.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

cAMP and Ca2+ act co-operatively on the Cl- conductance of HT29 cells.

Previous studies in HT29 cells have revealed that the Cl- channels induced by cAMP or by increasing cytosolic Ca2+, e.g. by addition of ATP, and by hypotonic cell swelling share in common all examined properties, such as ion selectivity and blocker sensitivity. In addition, it was shown that conductances induced by either pathway were not additive. Therefore all three pathways apparently act on the same type of small conductance Cl- channel. In CFPAC-1 cells the general properties of the Cl- conductance were identical. However, the cAMP response was absent. In both cell types the Ca(2+)-mediated conductance response was transient. Here we examine the kinetics of the conductance increases induced by neurotensin (NT, 10(-8) mol/l) or ATP (10(-5) mol/l) in HT29 and CFPAC-1 cells using the slow (nystatin) or fast whole cell patch clamp technique, and we ask whether cAMP influences these kinetics. In the continuous presence of NT the conductance response in both cell types was very transient. It collapsed with a time constant (tau) of 39 (30-56 s) in HT29 and of 33 (27-41 s) in CFPAC-1 cells. The ATP response was also transient with a tau of 49 (42-57 s) in HT29 cells and 102 (77-152 s) in CFPAC-1 cells. Pre-treatment by membrane permeable cAMP (10(-3) mol/l) enhanced the baseline conductance in HT29 but not in CFPAC-1 cells. Furthermore, the ATP- and NT-induced conductance increases became significantly less transient in HT29 but not in CFPAC-1 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1992

Active NaCl transport in the cortical thick ascending limb of Henle's loop of the mouse does not require the presence of bicarbonate.

The aim of the present study was to investigate whether bicarbonate buffer (CO2 + HCO3-) is required to sustain maximal NaCl transport in the cortical thick ascending limb of Henle's loop (cTAL) of the mouse. Transepithelial Na+ and Cl- net fluxes (JNa, JCl, pmol min-1 mm-1), measured by electron microprobe analysis, were similar irrespective of the presence or absence of CO2 + HCO3- in luminal and bathing solutions (JNaCl with CO2 + HCO3- = 203 +/- 25 pmol min-1 mm-1; JNaCl without CO2 + HCO3- = 213 +/- 13 pmol min-1 mm-1, n = 14). Furthermore the transepithelial potential difference, Vte, the transepithelial resistance, Rte, and the basolateral membrane potential, Vbl, were unaffected by CO2 + HCO3-. In the absence of CO2 + HCO3-, Vte was +17.0 +/- 1.7 mV (n = 9) (lumen positive), Rte was 28 +/- 2 omega cm2 (n = 9) and Vbl was -76 +/- 4 mV (n = 6). In the presence of CO2 + HCO3-, Vte, Rte and Vbl were +15.9 +/- 1.5 mV, 29 +/- 1 omega cm2 and -73 +/- 5 mV, respectively. 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid (SITS; 0.1 mmol l-1) and amiloride (1 mmol l-1) added to the (CO2 + HCO3-)-containing lumen perfusate were without effect on Vte and Rte. Finally, the effect of furosemide (0.1 mmol l-1) on Vte and Vbl in the presence of CO2 + HCO3- was investigated. Furosemide reversibly decreased Vte from +13.7 +/- 1.1 mV to +1.7 +/- 0.7 mV (n = 6) and hyperpolarized Vbl from -70 +/- 1 to -89 +/- 3 mV (n = 5), suggesting passive distribution of Cl- across the basolateral membrane. In conclusion, these data suggest that active NaCl transport in the cTAL of the mouse does not require the presence of CO2 + HCO3-.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1992

Transmitter-induced changes of the membrane voltage of HT29 cells.

The colonic carcinoma cell line HT29 was used to examine the influence of agonists increasing cytosolic cAMP and Ca2+ activity on the conductances and the cell membrane voltage (Vm). HT29 cells were grown on glass cover-slips. Cells were impaled by microelectrodes 4-10 days after seeding, when they had formed large plaques. In 181 impalements Vm was -51 +/- 1 mV. An increase in bath K+ concentration from 3.6 mmol/l to 18.6 mmol/l or 0.5 mmol/l Ba2+ depolarized the cells by 10 +/- 1 mV (n = 49) or by 9 +/- 2 mV (n = 3), respectively. A decrease of bath Cl- concentration from 145 to 30 mmol/l depolarized the cells by 11 +/- 1 mV (n = 24). Agents increasing intracellular cAMP such as isobutylmethylxanthine (0.1 mmol/l), forskolin (10 mumol/l) or isoprenaline (10 mumol/l) depolarized the cells by 6 +/- 1 (n = 13), 15 +/- 3 (n = 5) and 6 +/- 2 (n = 3) mV, respectively. In hypoosmolar solutions (225 mosmol/l) cells depolarized by 9 +/- 1 mV (n = 6). Purine and pyrimidine nucleotides depolarized the cells dose-dependently with the following potency sequence: UTP greater than ATP greater than ITP greater than GTP greater than TTP greater than CTP = 0. The depolarization by ATP was stronger than that by ADP and adenosine. The muscarinic agonist carbachol led to a sustained depolarization by 27 +/- 6 mV (n = 5) at 0.1 mmol/l, and to a transient depolarization by 12 +/- 4 mV (n = 5) at 10 mumol/l. Neurotensin depolarized with a half-maximal effect at around 5 nmol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗
PubMed1992

cAMP-dependent activation of small-conductance Cl- channels in HT29 colon carcinoma cells.

The present study was performed to examine the conductance properties in the colon carcinoma cell line HT29 and the activation of Cl- channels by cAMP. A modified cell-attached nystatin patch-clamp technique was used, allowing for the simultaneous recording of the cell membrane potential (PD) and the conductance properties of the cell-attached membrane. In resting cells, PD was -56 +/- 0.4 mV (n = 294). Changing the respective ion concentrations in the bath indicate that these cells possess a dominating K+ conductance and a smaller Cl- conductance. A significant non-selective cation conductance, which could not be inhibited by amiloride, was only observed in cells examined early after plating. The K+ conductance was reversibly inhibited by 1 - 5 mmol/l Ba2+. Stimulation of the cells by the secretagogues isoproterenol and vasointestinal polypeptide (VIP) depolarized PD and induced a Cl- conductance. Similar results were obtained with compounds increasing cytosolic cAMP: forskolin, 3-isobutyl-1-methylxanthine, cholera toxin and 8-bromoadenosine cyclic 3',5'-monophosphate (8-Br-cAMP). VIP (1 nmol/l, n = 10) and isoproterenol (1 mumol/l, n = 12) depolarized the cells dose-dependently and reversibly by 12 +/- 2 mV and 13 +/- 2 mV. The maximal depolarization was reached after some 20 s. The depolarization was due to increases in the fractional Cl- conductance. Simultaneously the conductance of the cell-attached membrane increased from 155 +/- 31 pS to 253 +/- 40 pS (VIP, n = 4) and from 170 +/- 43 pS to 268 +/- 56 pS (isoproterenol, n = 11), reflecting the gating of Cl- channels in the cell-attached membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Agonists↗
PubMed1992

Small-conductance Cl- channels in HT29 cells: activation by Ca2+, hypotonic cell swelling and 8-Br-cGMP.

The present study demonstrates the activation of Cl- channels in HT29 cells by agonist (ATP, neurotensin, carbachol) increasing cytosolic Ca2+, by hypotonic cell swelling and by cGMP. Cell-attached nystatin patch-clamp (CAN) as well as slow and fast whole-cell recordings were used. The cell membrane potential was depolarized in a dose-dependent manner with half-maximal effects at 0.4 mumol/l for ATP, 60 pmol/l for neurotensin and 0.8 mumol/l for carbachol. The depolarization, which was caused by Cl- conductances increases, occurred within 1 s and was accompanied by a simultaneous and reversible increase of the input conductance of the cell-attached membrane from 295 +/- 32 pS to 1180 +/- 271 pS (ATP; 10 mumol/l, n = 21) and 192 +/- 37 pS to 443 +/- 128 pS (neurotensin; 1 nmol/l, n = 8). The effects of the agonists could be mimicked by ionomycin (0.2 mumol/l), suggesting that an increase in intracellular Ca2+ was responsible for the activation of Cl- channels. The depolarization was followed by a secondary hyperpolarization. Hypotonic cell swelling also depolarized the cells and induced an increase in the membrane conductance. With 120 mmol/l NaCl the depolarization was 10 +/- 0.8 mV and the cell-attached conductance increased from 228 +/- 29 pS to 410 +/- 65 (n = 26) pS. NaCl at 90 mmol/l and 72.5 mmol/l had even stronger effects. Comparable conductance increases were also obtained when the different agonists or hypotonic cell swelling were examined in whole cell experiments. 5-Nitro-2-(3-phenylpropylamino)-benzoate (1 mumol/l) did not prevent the effects of Ca(2+)-increasing hormones and of hypotonic solutions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1992

Properties of the potassium conductances of principal cells of rat cortical collecting ducts.

In this study we examined by impalement techniques properties of the macroscopic K+ conductances in the luminal and basolateral membrane of principal cells from isolated perfused cortical collecting ducts (CCD) of the rat. Both membranes possess a dominating K+ conductance. Compared to their behaviour with K+, both membranes appear much less permeable to NH+4 and Rb+, and the K+ conductances of both membranes are inhibited by these cations. In light of these findings, it is very unlikely that significant amounts of NH+4, which is secreted in the CCD, cross the principal cells as NH+4. Several inhibitors with known effects on K+ channels in patch-clamp studies have been examined. Tetraethylammonium, which inhibits the excised K+ channels of these cells, has no effect on the macroscopic K+ conductances of either membrane. Verapamil, which inhibits the K+ channels in the luminal membrane, acts predominantly on the basolateral membrane K+ conductance in the intact tubule. Therefore, some of the macroscopic properties of the K+ conductances are distinct from those of single channels thus far observed in patch-clamp studies.

Animals↗
PubMed1992

Design, synthesis and biological activity of a series of torasemide derivatives, potent blockers of the Na+ 2Cl- K+ co-transporter: in-vitro study.

Pharmacomodulation of the torasemide molecule, a loop diuretic inhibiting Na+ 2Cl- K+ co-transport in the thick ascending limb of the loop of Henlé has been performed in order to obtain new long-acting diuretics. The aim of this study was to decrease the metabolism of the drug and to slow down its rate of excretion by increasing its hydrophobicity. The present study describes the synthesis and the inhibitory potency of new torasemide derivatives in the bioassay system of the cortical thick ascending limb of rabbit. A correlation between the lipophilicity (log P') of these substances and their activity as inhibitors of the Na+ Cl- K+ co-transporter was observed. The present design led to compounds more active than torasemide. Structure-activity relationships permit us to propose an interaction model between torasemide derivatives and the Na+ 2Cl- K+ co-transport system of the cortical thick ascending limb.

Animals↗
PubMed1992

Chemical probes for anion transporters of mammalian cell membranes.

Mammalian cell membranes harbor several types of chloride channels, chloride-cation symporters/cotransporters, and several classes of anion exchangers/antiporters. These transport systems subserve different cellular or organismic functions, depending on the nature of the cell, the spatial organization of transporters, and their functional interplay. Chemical probing has played a central role in the structural and functional delineation of the various anion transport systems. The design of specific probes or their selection from existing sources coupled with their judicious application to the most appropriate biological system had led to the identification of specific anion transporters and to the elucidation of the underlying molecular transport mechanism. In many instances, chemical probing has remained the major or exclusive analytical tool for the functional definition or identification of a given transport system, particularly for discerning among the various anion transporters which operate in highly heterogeneous cell membrane systems. This work critically reviews the present state of the chemical armamentarium available for the most common anion transporters found in mammalian cell membranes. It encompasses the description of the most useful or commonly used probes in terms of their chemical, biochemical, physiological, and pharmacological properties. The review deals primarily with what chemical probes tell about anion transporters and, most importantly, with the limitations inherent in the use of probes in transport studies.

Animals↗
PubMed1992

Action of diuretics at the cellular level.

Classification of diuretics is based on their site and mechanism of action in the nephron. The most frequently used substances comprise 1. the mostly proximally acting carbonic anhydrase inhibitors (CAI); 2. the loop diuretics (LD); 3. the early distally acting thiazides (TZ); and 4. the K+ sparing diuretics (KS) acting in the distal tubule. CAI such as acetazolamide inhibit the dehydration of H2CO3 at the luminal membrane, the hydration of CO2 within the proximal tubule cell and the exit of HCO-3 out of the cell. As a result of this proximal reabsorption of HCO-3 is reduced, a slight diuresis and saluresis is induced. The enhanced urinary excretion of HCO-3 will cause a metabolic acidosis. LD inhibit the Na+2Cl-K+ carrier in the thick ascending limb of the loop of Henle (TAL). This produces a marked diuresis and saluresis which is accompanied by enhanced Ca2+, Mg2+, K+ and acid excretion. TZ inhibit the Na+Cl- cotransporter in the early distal tubule. The diuresis is less marked than that induced by LD but the renal losses of K+ are comparable. KS inhibit Na+ channels present in the luminal membrane of the cortical collecting tubule. This leads to a very limited diuresis, but a marked attentuation of renal K+ losses. All diuretics act by inhibiting the admission of Na+ (LD, TZ, KS) or HCO-3 (CAI) into the cell. Their organotropy is merely due to the fact that they are concentrated in tubule fluid by volume reabsorption and by proximal tubule secretion.

Animals↗
PubMed1991

Different types of blockers of the intermediate-conductance outwardly rectifying chloride channel in epithelia.

Epithelial chloride channels can be blocked by various inhibitors, which show considerable differences in their molecular structure. In the present patch-clamp study, we compared different blockers of one type of epithelial Cl- channel with respect to their inhibitory potency. We applied the blockers to excised inside-out-or outside-out-oriented membrane patches of cultured HT29 colon carcinoma and respiratory epithelial cells (REC) containing the outwardly rectifying intermediate-conductance (ICOR) chloride channel. Four types of inhibitory compounds were tested: stilbene disulphonate derivatives, indanyloxyacetic acid, amidine, and arylaminobenzoates. The concentrations for half-maximal inhibition (IC50) for the different channel blockers were (mumol/l): 4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulphonic acid 100; 4,4'-diisothiocyanato-stilbene-2,2'-disulphonic acid 80; indanyloxyacetic acid 9; 4,4'-dinitrostilbene-2,2'-disulphonic acid 8; amidine 8 and 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) 0.9. All compounds, when applied to the cytosolic side of the channel, induced a flicker-type block of the ICOR Cl- channel at lower concentrations and a complete channel inhibition at higher concentrations. The inhibitory potency of NPPB was much higher when it was added to the external surface of the channel in outside-out-oriented membrane patches. At 1 mumol/l the inhibition was complete. All blocker effects were fully reversible. The probe with the highest affinity (NPPB) and a closely related compound 5-nitro-2-(3-phenylethylamino)-benzoate (NPEB) were used to construct macromolecular probes by linking these blockers to aminopolyethyleneglycol (PEG) or amino-ethyl-O-dextran (5 kDa).2+ These macromolecular NPPB and NPEB derivatives inhibited the ICOR Cl- channels only from the outside but had no effect on the cytosolic side.(ABSTRACT TRUNCATED AT 250 WORDS)

Amidines↗
PubMed1991

Bicarbonate permeability of epithelial chloride channels.

Bicarbonate permeability of epithelial chloride channels has been studied using the patch-clamp technique. The experiments were performed in excised inside-out oriented membrane patches from three different cultured cell types: (a) HT29 colon carcinoma cell line, (b) T84 colon carcinoma cell line, and (c) respiratory epithelial cells (REC) in primary culture. In all three preparations we observed outwardly rectifying chloride channels with similar conductances with 145 mmol/l NaCl solution in the pipette and in the bath (Cl- pipette/Cl- bath). When Cl- was replaced by HCO3- in the bath (Cl-/HCO3-) the conductance of the channel at negative clamp voltages was reduced significantly by 40% for HT29 (n = 6), 39% for T84 (n = 7), and 38% for REC (n = 6). Similarly, the zero-current potential (V1 = 0) was shifted from 0 mV (Cl-/Cl-) to negative values (Cl-/HCO3-) revealing permeability ratios PCl/PHCO3 of 2.4 +/- 0.1 for HT29 (n = 6), 2.0 +/- 0.1 for T84 (n = 7), and 1.8 +/- 0.1 for REC (n = 7). With NaHCO3 as the pipette solution and NaCl in the bath, the V1 = 0 was positive and a PCl/PHCO3 value of 2.3 +/- 0.1 was determined for HT29 (n = 5). Replacement of Cl- in the bath by HCO3- reduced V1 = 0 to values close to 0 mV. In another series of experiments, the pipette was filled with 145 mmol/l NaCl and the bath contained 35 mmol/l NaCl to which 35 mmol/l NaHCO3 were added. We found that neither the conductance for the inward current nor V1 = 0 was changed significantly with the addition of NaHCO3 (HT29, n = 6). We conclude that the HCO3- permeability and HCO3- conductance of these channels is about half of that for Cl-.

Bicarbonates↗
PubMed1991

Antidiuretic hormone acts via V1 receptors on intracellular calcium in the isolated perfused rabbit cortical thick ascending limb.

The effect of antidiuretic hormone [( Arg]vasopressin, ADH) on intracellular calcium activity [Ca2+]i of isolated perfused rabbit cortical thick ascending limb (cTAL) segments was investigated with the calcium fluorescent dye fura-2. The fluorescence emission ratio at 500-530 nm (R) was monitored as a measure of [Ca2+]i after excitation at 335 nm and 380 nm. In addition the transepithelial potential difference (PDte) and transepithelial resistance (Rte) of the tubule were measured simultaneously. After addition of ADH (1-4 nmol/l) to the basolateral side of the cTAL R increased rapidly, but transiently, from 0.84 +/- 0.05 to 1.36 +/- 0.08 (n = 46). Subsequently, within 7-12 min R fell to control values even in the continued presence of ADH. The increase in R evoked by the ADH application corresponded to a rise of [Ca2+]i from a basal level of 155 +/- 23 nmol/l [Ca2+]i up to 429 +/- 53 nmol/l [Ca2+]i at the peak of the transient, as estimated by intra- or extracellular calibration procedures. The electrical parameters (PDte and Rte) of the tubules were not changed by ADH. The ADH-induced Ca2+ transient was dependent on the presence of Ca2+ on the basolateral side, whereas luminal Ca2+ had no effect. d(CH2)5[Tyr(Me)2]2,Arg8vasopressin, a V1 antagonist (Manning compound, 10 nmol/l), blocked the ADH effect on [Ca2+]i completely (n = 5). The V2 agonist 1-desamino-[D-Arg8]vasopressin (10 nmol/l, n = 4), and the cAMP analogues, dibutyryl-cAMP (400 mumol/l, n = 4), 8-(4-chlorophenylthio)-cAMP (100 mumol/l, n = 1) or 8-bromo-cAMP (200 mumol/l, n = 4) had no influence on [Ca2+]i. The ADH-induced [Ca2+]i increase was not sensitive to the calcium-channel blockers nifedipine and verapamil (100 mumol/l, n = 4). We conclude that ADH acts via V1 receptors to increase cytosolic calcium activity transiently in rabbit cortical thick ascending limb segments, possibly by an initial Ca2+ release from intracellular stores and by further Ca2+ influx through Ca2+ channels in the basolateral membrane. These channels are insensitive to L-type Ca2+ channel blockers, e.g. nifedipine and verapamil.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1991

Effects of arylaminobenzoate-type chloride channel blockers on equivalent short-circuit current in rabbit colon.

Arylaminobenzoates were examined in rabbit colon mounted in an Ussing chamber. The open-circuit transepithelial voltage (Vte) and resistance (Rte) were measured and the equivalent short-circuit current (Isc = Vte/Rte) was calculated. After serosal (s) and mucosal (m) addition of indomethacin (1 mumol/l) Isc was -71 +/- 11 (n = 118) microA/cm2. Amiloride (0.1 mmol/l, m) inhibited this current and reversed the polarity to +32 +/- 4 (n = 118) microA/cm2. In the presence of amiloride and indomethacin, prostaglandin E2 (1 mumol/l, s), known to induce Cl- secretion, generated an Isc of -143 +/- 8 (n = 92) microA/cm2. The arylaminobenzoate and Cl- channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) reduced Isc reversibly with a half-maximal inhibition (IC50) at approximately 0.35 mmol/l and 0.2 mmol/l for mucosal and serosal application respectively. To test whether the poor effect was caused by mucus covering the luminal surface, dose/response curves of the mucosal effect were repeated after several pretreatments. Acidic pH on the mucosal side reduced IC50 to approximately 0.1 mmol/l. A similar effect was observed after N-acetyl-L-cysteine (m) preincubation. Pretreatment with N-acetyl-L-cysteine (m) and carbachol (s), in order to exhaust mucus secretion, and L-homocysteine (m) were more effective and reduced IC50 to approximately 50 mumol/l. To test whether this effect of NPPB was caused by non-specific effects, the two enantiomers of 5-nitro-2-(+/-1-phenylethylamino)-benzoate were tested of which only the (+) form inhibited the Cl- conductance in the thick ascending limb of the loop of Henle (TAL).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗