EXPRESSION OF CL- HCO3- EXCHANGER IN THE BASOLATERAL MEMBRANE OF MOUSE MEDULLARY THICK ASCENDING LIMB/

Although a basolatural Cl-/HCO3- exchanger(AE) has been implicate ill the arginine vasopressin (AVP)-dependent hypertonic regulatory increas e in the medullary thick ascending limb (MTAL), there are conflicting data regarding whether this exchanger is indeed present in this tubule segment. In this study, mouse MTAL was examined whether CL-/HCO3- exc hange activity was present in the basolateral membrane and whether mRN As from the known AE genes are expressed. Cl-/HCO3- exchange activity was examined in isolated perfused MTAL tubules under isotonic conditio ns and in the absence of arginine vasopressin. 2',7'-Bis(2-carboxyethy l)-5(6)-carboxyfluorescein was used to monitor intracellular pH. Remov al of basolateral Cl- induced reversible cell alkalization that was in dependent of external Na+ and completely inhibited by peritubular 4,-4 '-diisothiocyanostilbene-2,2'-disulfonic acid (200 mu M). The role and extent of cell alkalinization were significantly greater in the prese nce than absence of external CO2/HCO3-. A voltage clamp did not inhibi t cell alkalinization induced by basolateral Cl- removal. Consistently , addition of basolateral CI-induced reversible cell acidification in MTAL depleted of intracellular Cl-. Furthermore, mRNA encoding two mem bers (AE2 and AE3) of the AE gene family were demonstrated in microdis sected mouse MTAL tubules by reverse transcription-polymerase chain re action. It is concluded that AE is present in the basolateral membrane of mouse MTAL.