Ruiz O S, Qiu Y Y, Arruda J A
Section of Nephrology, University of Illinois at Chicago, 60612, USA.
Proc Soc Exp Biol Med. 1996 Feb;211(2):199-204. doi: 10.3181/00379727-211-43962.
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 Km for Na of 20 mM, was electrogenic and 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.
