Intracellular pH regulation in the renal proximal tubule of the salamander. Basolateral HCO3- transport.

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Abstract
PH-, Na- and Cl-sensitive microelectrodes were used to study basolateral HCO3- transport in isolated, perfused proximal tubules of the tiger salamander A. tigrinum. In 1 series of experiments, basolateral pH (pHb) was lowered from 7.5-6.8 by reducing [HCO3-]b from 10 to 2 mM at a constant PCO2 [partial pressure of CO2]. This reduction of pHb and [HCO3-]b causes a large (.apprx. 0.35), rapid fall in pHi [interval pH] and a transient depolarization of the basolateral membrane. Returning pHb and [HCO3-]b to normal has the opposite effects. Similar reductions of luminal pH (pHl) and [HCO3-]l have only minor effects. The reduction of [HCO3-]b and pHb also produces a reversible fall in .**GRAPHIC**. [intracellular Na activity]. In a 2nd series of experiments, [Na+]b was reduced at constant [HCO3-]b and pHb, and a rapid fall was observed in pHi and a transient basolateral depolarization. These changes are reversed by returning [Na+]b to normal. The effects of altering [Na+]l in the presence of HCO3- or of altering [Na+]b in the nominal absence of HCO3- are substantially less. Although the effects on pHi and basolateral membrane potential of altering either [HCO3-]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 .**GRAPHIC**. consistent with a tight linkage between Cl- fluxes and those of Na+ and HCO3-. These changes are apparently mediated by a single transport system, not involving Cl-. Apparently, HCO3- transport is restricted to the basolaterl membrane, and HCO3- fluxes are linked to those of Na+. Data are compatible with an electrogenic Na/HCO3 transporter that carries Na+, HCO3-, and net negative charge in the same direction.

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