The Renal Cortical Na-HCO 3 Cotransporter: V. Expression in Xenopus Oocytes

Abstract

Abstract

The Na-HCO₃ cotransporter is the main system responsible for HCO₃ transport from proximal tubule cells into the blood. The expression of the renal cortical basolateral Na-HCO₃ cotransporter was studied in Xenopus laevis oocytes. Injection of mRNA prepared from renal cortex into oocytes enhanced HCO₃-dependent ²²Na uptake, on average 6-fold, (range: 2–44) compared with vehicle-injected oocytes, without altering ²²Na uptake in presence of gluconate. These findings indicate that mRNA selectively expresses Na-HCO₃ cotransporter activity without altering diffusive ²²Na uptake. The expressed Na-HCO₃ cotransporter activity had a K _m for Na of 20 mM, was electrogenic and was sensitive to disulfonic stilbenes. In presence of HCO₃, the expressed Na-HCO₃ cotransporter activity was like the native cotransporter, enhanced by carbonate or sulfite, a finding compatible with the existence of distinct sites for HCO₃ and carbonate on the transport system. After fractionation by a sucrose density gradient, the mRNA fraction responsible for the Na-HCO₃ cotransporter was found to be between 1.50 and 3.48 kb classes. [P.S.E.B.M. 1996, Vol 211]