DIFFERENTIAL REGULATION OF MEMBRANE-POTENTIAL AND CONDUCTANCE VIA INTRACELLULAR AND EXTRACELLULAR PH IN FUSED PROXIMAL TUBULAR CELLS OF FROG KIDNEY

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