Peritubular buffering power and luminal acidification in proximal convoluted tubules of the rat.

Proximal tubular acidification was studied varying peritubular buffer concentration as well as the nature of the main peritubular buffer system. Two buffer systems were used: phosphate which varied between 1 and 20 mM, and glycodiazine, at 5 and 20 mM. Luminal perfusate was always 20 mM phosphate Ringer's. Acidification half times increased as peritubular buffer concentration decreased, independently of the nature of the buffer. At 1 mM phosphate, net H-ion flux (JH +) was 0.53 nmol . cm-2 . s-1; at 5 mM it was 0.73 nmol . cm-2 . s-1 and at 20 mM, 0.97 nmol . cm-2 . s-1. When the peritubular buffer was glycodiazine, JH + was 0.77 nmol . cm-2 . s-1 at 5 mM peritubular buffer concentration and 0.99 nmol . cm-2 . s-1 at 20 mM. Acetazolamide (10(-4) M) and DIDS (10(-4) M) both abolished the effect of peritubular buffer concentration changes on acidification half times. It was shown that these effects were related to the capacity of the peritubular buffer to attenuate changes in peritubular pH as consequence of base transfer by the peritubular membrane. Peritubular buffering power could act limiting intracellular pH increments consequent to luminal H-ion secretion.