Distal tubular acidification in the remnant kidney

The present studies examined the effect of three-fourths nephrectomy on the rate of acidification, i.e., total CO₂ (tCO₂) absorption (J(tCO₂)) in the superficial distal tubule of the rat. Total glomerular filtration rate following three-fourths nephrectomy was 1.29 ± 0.06 vs. 3.29 ± 0.08 ml/min in sham controls, P < 0.001. Systemic acid-base parameters were the same in both groups, but urine pH was lower in nephrectomized rats. In vivo microperfusion with identical isohydric solutions revealed that the J(tCO₂), fluid absorption (J(v)), lumen-negative transepithelial potential difference (V(T)) were all significantly greater in the distal tubule of remnant kidneys. As the relative increase in J(v) exceeded J(tCO₂), the perfusate tCO₂ concentration increased markedly in remnant kidney distal tubules from 30.3 ± 0.59 to 39.9 ± 1.73 mM. To determine if the increase in tCO₂ concentration accounted for the difference in J(tCO₂), a second control group was studied using a perfusate tCO₂ concentration of 39.6 ± 0.79 mM. Distal tubular J(tCO₂), J(v), and V(T) were significantly less in this control group than in the remnant kidney group. In separate studies, 10^-4 M amiloride was added to the perfusate used in remnant kidneys and controls studied with the elevated perfusate tCO₂ concentration. The addition of 10^-4 M amiloride to the perfusate reduced V(T) and J(tCO₂). At identical values for V(T), J(tCO₂) was higher in the distal tubule of remnant kidneys than in controls. We conclude the following. 1) The rate of acidification is increased in the distal tubule or remnant kidneys. This increase in acidification presumably contributes to the maintenance of systemic acid-base balance in this experimental model. 2) The measured increase in distal tubular J(tCO₂) in the remnant kidney relative to controls in these studies was not dependent on a more favorable electrical gradient for proton secretion.