Expression of rat renal Na+HCO3-cotransporter in Xenopus laevis oocytes

The goal of this study was to determine whether Na+HCO3- cotransport from rat renal cortex can be functionally expressed in Xenopus laevis oocytes. Using a two electrode voltage-clamp device, HCO(3-)-dependent currents were determined as the difference in current measured in a nominally HCO(3-)-free buffer, pH 7.5 and a buffer with 30 mmol/l HCO3-, pCO2 5.33 kPa, pH 7.5. The size of renal cortex mRNA required to express maximum HCO(3-)-dependent current was 2-3 kb. The expressed current depended on Na+ and was sensitive to 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and acetazolamide (each 1 mmol/l), inhibitors known to block the native Na(+)HCO3- cotransporter in several tissues including rat proximal tubule. Water-injected oocytes did not show any measurable response either to increased HCO3- nor to Na(+)-free perfusion or to the inhibitors, indicating the absence of an endogenous electrogenic HCO3-transporter. Our data indicate that the rat renal mRNA of 2-3 kb size contains the message for the Na+HCO3-cotransporter.