Acetazolamide inhibition of basolateral Cl-/HCO3- exchange in rabbit renal proximal tubule S3 segment.
Cell pH (pH(i)) and cell membrane potential (Vb) were measured in isolated S3 segments of rabbit renal proximal tubule with double-barrelled microelectrodes to search for a possible effect of the carbonic anhydrase inhibitor, acetazolamide (ACZ), on Cl-/HCO3- exchange in the basolateral cell membrane. ACZ was found to retard and reduce the pH(i) response to bath Cl- removal reversibly with half-maximal inhibition at 0.42 mmol/l and a rather flat concentration dependence (Hill coefficient approximately 0.36). To determine whether the retardation resulted from inhibition of cytoplasmic carbonic anhydrase, which might have delayed the attainment of HCO3-/CO2 equilibrium, we have measured the response of pH(i) to step changes in PCO2 in the presence and absence of ACZ. ACZ greatly retarded the pH(i) response to CO2 steps; however, the concentration dependence differed (half-maximal inhibition at 18 mumol/l) and even at maximal ACZ concentrations the response to CO2 steps was more than twice as fast as the response to Cl- replacement. Since, in addition, the ACZ inhibition of Cl-/HCO3- exchange could not be overcome by increasing PCO2 we conclude that the ACZ effect on Cl-/HCO3- exchange in rabbit proximal tubule S3 segments does not result from inhibition of cytosolic or membrane-bound carbonic anhydrase, but from a direct interaction with the exchanger molecule.
Seki
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Zentrum der Physiologie, J.W. Goethe Universität, Frankfurt/Main, Federal Republic of Germany.
Frömter
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D000086:Acetazolamide / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D002245:Carbon Dioxide / Q000494:pharmacology; D002352:Carrier Proteins / Q000037:antagonists & inhibitors*; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000494:pharmacology; D005260:Female; D005942:Gluconates / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D010313:Partial Pressure; D011817:Rabbits
D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D005942:Gluconates; D002245:Carbon Dioxide; D000086:Acetazolamide; C030691:gluconic acid