The present study examined acidification mechanisms on the basolateral membrane of the early renal vesicle, an undifferentiated ball of cells that will develop into parts of the glomerulus, proximal tubule, loop of Henle, and a portion of the distal convoluted tubule. Renal vesicles were dissected from newborn rabbit kidneys and bathed in vitro. To examine the basolateral membrane acidification mechanisms, intracellular pH (pHi) was measured by use of the pH-sensitive dye (2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. Evidence for Cl(-)-base exchange included the fact that removal of bath Cl-resulted in cell alkalinization (7.35 +/- 0.03 to 7.48 +/- 0.05; P less than 0.01). Cell alkalinization induced by Cl- removal was also observed in presence of a voltage clamp without bath Na+ (7.18 +/- 0.02 to 7.39 +/- 0.04; P less than 0.01) and was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). pHi recovery after acute alkalinization resulting from CO2 removal was 0.20 +/- 0.03 pH units/min in the presence of Cl-, 0.07 +/- 0.01 in experiments with 0.2 mM DIDS, and 0.07 +/- 0.01 in absence of bath Cl-. The early renal vesicle also has a basolateral Na(+)-H+ antiporter. Removal of bath Na+ resulted in cell acidification (7.36 +/- 0.09 to 7.18 +/- 0.06; P less than 0.01), which was inhibited by 2 mM amiloride. Cell pH recovery after acute acidification (NH4Cl prepulse technique) was entirely dependent on bath Na+ and inhibited by amiloride. Thus the renal vesicle has basolateral membrane Na(+)-H+ and Cl(-)-base exchangers that can defend against cell acidification and alkalinization, respectively.