Intracellular pH regulation in the renal proximal tubule of the salamander: Basolateral HCO−3 transport

Abstract

We have used pH-, Na-, and Cl-sensitive microelectrodes to study basolateral HC03 transport in isolated, perfused proximal tubules of the tiger salamander Ambystoma tigrinum. In one series of experiments, we lowered basolateral pH (pHb) from 7.5 to 6.8 by reducing [HCO−3]]b from 10 to 2 mM at a constant pCO2. This reduction of pHb and [HCO−3]]b causes a large (~0.35), rapid fall in pHi as well as a transient depolarization of the basolateral membrane. Returning pHb and [HC03]b to normal has the opposite effects. Similar reductions of luminal pH (pHI) and [HCO−3]i have only minor effects. The reduction of [HCO−3]b and pHb also produces a reversible fall in a Na. In a second series of experiments, we reduced [Na+]b at constant [HC03]b and pHb, and also observed a rapid fall in pHi and a transient basolateral depolarization. These changes are reversed by returning [Na+]b to normal. Theeffects of altering [Na+]i in the presence of HC03, or of altering [Na+]b in the nominal absence 6f HC03, are substantially less. Although the effects on pHi and basolateral membrane potential of altering either [HCO−3]]b or [Na+]b are largely blocked by 4-acetamido-4-isothiocyanostilbene-2,2'-disulfonate (SITS), they are not affected by removal of Cl−, nor are there accompanying changes in aiC1 consistent with a tight linkage between Cl− fluxes and those of Na+ and HCOS. The aforementioned changes are apparently mediated by a single transport system, not involving Cl−. We conclude that HC0−3 transport is restricted to the basolateral membrane, and that HC03 fluxes are linked to those of Na+. The data are compatible with an electrogenic Na/HC0−3 transporter that carries Na+, HCOa, and net negative charge in the same direction. © 1983, Rockefeller University Press., All rights reserved.