Filtered load of buffer and renal H-ion secretion: mechanism of proximal tubule load dependence.

ABSTRACT

When the filtered load of buffers like bicarbonate or phosphate is increased by elevating GFR or buffer concentration in plasma, the overall renal reabsorption of bicarbonate or the formation of titratable acidity are markedly increased. The same happens when buffer concentration or flow rate are varied during proximal microperfusion. We have recently studied the mechanisms of this functional dependence. We have observed that the rate of bicarbonate reabsorption is always proportional to luminal buffer concentration when a stationary fluid column is injected into the proximal lumen. H-ion secretion is also proportional to luminal levels of non-bicarbonate buffers. Using a pH-stat technique adapted to renal tubules, we have shown that H-ion secretion is dependent on proximal pH independently of the used buffer species. A kinetic analysis of these data shows a non-linear relationship between luminal H+ and H+ secretion, compatible with carrier mediated transport.