Kidney epithelial cells of monkey origin (BSC-1) express a sodium bicarbonate cotransport. Characterization by 22Na+ flux measurements

Na movement across the plasma membranes of confluent monolayers of monkey kidney epithelial cells (BSC-1) was studied using 22Na+ uptake and efflux techniques in the presence of 10(-4) M ouabain. In the presence of 28 mM bicarbonate, uptake was inhibited by both 10(-3) M amiloride and 10(-3) M 4,4'diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). In DIDS-pretreated cells, 10(-3) M amiloride led to a further reduction of 22Na+ uptake, while 10(-5) furosemide was ineffective. DIDS also inhibited sodium efflux, indicating that the DIDS-sensitive pathway mediates both influx and efflux of 22Na+. DIDS-sensitive 22Na+ uptake, as studied in the presence of both 10(-4) M ouabain and 10(-3) M amiloride, was abolished by the absence of bicarbonate, which could not be substituted by other plasma membrane-permeable buffers. In 28 mM HCO3-, DIDS-sensitive uptake of 28 mM Na+ was cis-inhibited by 124 mM Na+, but no significant inhibition by K+ or Li+ was found. DIDS-sensitive 22Na+ uptake was a saturable function of both Na+ concentration (apparent Km between 20 and 40 mM at 28 mM HCO3-) and HCO3- concentration (apparent Km between 7 and 14 mM at 151 mM Na+). Intracellular microelectrode measurements showed that net Na+ transport in the presence of HCO3- is electrogenic, i.e. that there is anion cotransport with Na+. This effect is abolished by 1 mM DIDS. It is concluded that monkey kidney epithelial cells possess a stilbene-sensitive, electrogenic sodium bicarbonate symport, which may play an important role in bicarbonate reabsorption in the mammalian kidney.