Kinetic study of bicarbonate reabsorption in proximal tubule of the rat.

MALNIC, GERHARD, AND MARGARIDA DE MELLO-AIRES. Kinetic study of bicarbonate reabsorption in proximal tubule of the rat. Am. J. Physiol. 220(6) : 1759-1767. 197 1 .-Continuous recording of tubular pH was performed during stopped-flow microperfusion of rat proximal tubules with isotonic solutions containing 25 or 100 mEq/liter HCO 3, by means of an antimony microelectrode. After stabilization of pH values, lower pH and HCO,were found than during free flow in control rats. In acetazolamide-infused rats, pH was higher and bicarbonate lower than during free flow, but both values were significantly higher than controls. The velocity of acidification was decomposed into two phases, a first, rapid one, and a second, slower phase. The first phase was shown to depend on CO2 diffusion. It disappeared upon perfusion with a solution preequilibrated with CO2 . The second phase, evaluated by transformation of the pH values into bicarbonate concentrations, had a half-time of 3-4 sec. It was not significantly altered by substitution of choline for sodium, but was considerably retarded in acetazolamide-infused rats. Only one process of bicarbonate reabsorption was apparent, whose rate is about halved by acetazolamide. Its maximal rate may approach that of sodium chloride.