Expression of Cl-/HCO3- exchanger in the basolateral membrane of mouse medullary thick ascending limb.

Although a basolateral Cl-/HCO3- exchanger (AE) has been implicated in the arginine vasopressin (AVP)-dependent hypertonic regulatory increase 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- exchange activity was present in the basolateral membrane and whether mRNAs from the known AE genes are expressed. Cl-/HCO3- exchange activity was examined in isolated perfused MTAL tubules under isotonic conditions and in the absence of arginine vasopressin. 2',7'-Bis(2-carboxyethyl)-5(6)-carboxyfluorescein was used to monitor intracellular pH. Removal of basolateral Cl- induced reversible cell alkalization that was independent of external Na+ and completely inhibited by peritubular 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (200 microM). The rate and extent of cell alkalinization were significantly greater in the presence than absence of external CO2/HCO3-. A voltage clamp did not inhibit cell alkalinization induced by basolateral Cl- removal. Consistently, addition of basolateral Cl- induced reversible cell acidification in MTAL depleted of intracellular Cl-. Furthermore, mRNA encoding two members (AE2 and AE3) of the AE gene family were demonstrated in microdissected mouse MTAL tubules by reverse transcription-polymerase chain reaction. It is concluded that AE is present in the basolateral membrane of mouse MTAL.