Differential regulation of membrane potential and conductance via intra-and extracellular pH in fused proximal tubular cells of frog kidney

Abstract

Intracellular pH (pHi), membrane potential (Vm) and membrane conductance (Gm) in fused proximal tubular cells of the frog kidney, were determined at three extracellular pH (pHo) values, 7.5, 8.5 and 6.5. Imposed changes of pHo by +/- 1 pH unit induced parallel but smaller shifts of pHi. The alkaline milieu hyperpolarized the cells and increased Gm, whereas the acid milieu depolarized and lowered Gm. We subsequently introduced a weak acid and its conjugate base (acetic acid/acetate), or a weak base and its conjugate acid (NH3/NH4+), at pHo 7.5, 8.5 and 6.5 to shift pHi without altering pHo, or to shift pHi against imposed changes of pHo. From these experiments, we observed that under some circumstances Vm varied with pHo but without Gm or pHi changes, whereas under other circumstances changes of Gm occurred during alterations of pHi while pHo and Vm remained unaltered. At pHi approximately 6.5 associated with Vm approximately -10 mV, Gm dramatically increased to quasi-infinite values. This increase was not an artifact since Gm returned to its control value following recovery to the control solution or in the presence of hyperosmotic solution. In conclusion, we demonstrate a differential regulation whereby Vm and Gm are controlled by pHo and pHi: pHo modulates mainly Vm and pHi modulates chiefly Gm. Furthermore, at pHi approximately 6.5 and Vm approximately -10 mV, our data reveal a large Gm that tends towards infinite values in a reversible fashion.