The mechanism of acetate stimulation of PAH transport in rat kidney fragments.

Accumulation of p-aminohippurate (PAH) by rat kidney fragments incubating in vitro is enhanced as medium pH rises from 7.4 toward 7.8. Since medium pH increases from 7.4 to 7.8 over a 90-min period in the presence of acetate, we were unsure whether acetate had any direct stimulatory effect on transport. Rat renal fragments incubating in acetate showed no enhanced PAH accumulation at 30 and 60 min when medium pH was less than 7.6 but did increase approximately 25% after 90 min when pH approached 7.8. By a number of different procedures, we consistently found that when medium pH was not allowed to rise, acetate did not stimulate PAH accumulation. We conclude that at an initial pH of 7.4, acetate stimulation of PAH uptake by rat kidney fragments during the course of a 90-min incubation can be explained almost entirely by a rise in pH to a more optimal range for transport. In contrast, stimulation of PAH accumulation by lactate and pyruvate cannot be explained solely by changes in medium pH.