Effects of acetate on luminal acidification processes in the S3 segment of the rabbit proximal tubule.

We determined that, in the nominal absence of HCO-3, acetate (Ac-) doubles luminal acidification in the S3 segment of the rabbit proximal tubule. This stimulation had two components, one that was dependent on Na+ and luminal Ac- and a second that was independent of Na+ but dependent on basolateral Ac-. In the presence of 25 mM HCO-3, Ac- did not stimulate acid secretion (i.e., HCO-3 reabsorption), but actually inhibited it. The inhibition was 35% with bilateral Ac- and 15% with basolateral Ac-. The effects of Ac- were reversible both in the absence and presence of HCO-3, and are present at concentrations as low as 1 mM. We conclude that acetate (i.e., monocarboxylates) has a significant effect on luminal acidification processes both in the presence and absence of HCO-3.