The renal cortical Na-HCO3 cotransporter: V. expression in Xenopus oocytes.
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.
Ruiz
O S
OS
Section of Nephrology, University of Illinois at Chicago, 60612, USA.
Qiu
Y Y
YY
Arruda
J A
JA
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002352:Carrier Proteins / Q000032:analysis* / Q000235:genetics; D005260:Female; D007672:Kidney Cortex / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D027982:Sodium-Bicarbonate Symporters; D014982:Xenopus laevis
D001639:Bicarbonates; D002352:Carrier Proteins; D012333:RNA, Messenger; D027982:Sodium-Bicarbonate Symporters; D012964:Sodium