Effect of temperature on proximal tubular acidification

Abstract

The effect of temperature on proximal tubular acidification was studied in isolated rat kidney, perfused with 20 mM phosphate Ringer's containing 7.5 g/100 ml bovine albumin, equilibrated with air. Tubular pH was measured with Sb microelectrodes during stopped-flow microperfusion. The temperature of the kidney was varied between 10 and 46° C. At 10° C the proximal tubule was still able to maintain pH gradients of about 0.6 pH units. However, half-times (t/2) of both acidification and alkalinization were markedly increased, from 6–7 s at 37° C to 27–30 s at 10° C. In consequence, net H⁺-ion flux into the tubule was reduced to 26% of that at 37° C. In this system, in the absence of exogenous HCO ^-₃ and CO₂,t/2 of acidification and alkalinization were very similar at 37° C and below. Above 37° C alkalinizationt/2 fell markedly to 1.43±0.09 (11) s at 46° C, while acidificationt/2 stayed at about 7 s. H⁺-ion back-fluxes increased progressively from 10–46° C, while secretory J_H reached a maximal value at 37° C and fell at higher temperatures. Apparent activtion energies calculated from rate coefficients were 8.48 kcal·mol⁻¹ for acidification, and 9.30 for alkalinization, and those calculated from J_H were 6.30 and 9.55 respectively. These data indicate that both H-ion secretion and back-flux are carrier-mediated, probably flowing through the Na/H exchanger in the luminal membrane, since their activation energies are of the same order of magnitude and markedly higher than those for protons in solution.