Effect of benzolamide on pH in the proximal tubules and peritubular capillaries of the rat kidney.

The influence of carbonic anhydrase inhibition with benzolamide on proximal tubular and peritubular capillary pH was evaluated in the rat using a glass-membrane pH microelectrode. Control peritubular capillary pH, 7.38 +/- .02 (N=11), was significantly lower than control arterial pH, 7.44 +/- .01, p < .05. Early proximal tubular pH, 7.20 +/- .02 (N = 17), was more alkaline than late proximal tubular pH, 6.74 +/- .06 (N = 13), p < .001; pH at both sites was more acid than in the peritubular capillary, p < .001. Benzolamide treatment had no detectable effect on arterial or peritubular capillary pH, but reduced early proximal tubular pH by 0.54 pH units, to 6.66 +/- .04 (N = 13), p < .001. Late proximal pH also fell slightly to 6.57 +/- .03 (N = 14), p < .02. The results support previous observations indicating that benzolamide treatment decreases early proximal tubular pH dramatically, and provide further evidence that HCO3- reabsorption is accomplished by hydrogen ion secretion in the proximal tubule.