Sodium-proton exchanger in isolated hepatocytes exhibits a set point.

Na+-H+ exchange activity was examined in hepatocytes isolated from rat liver. Activity was measured as amiloride-sensitive fluorescence changes utilizing the pH-sensitive chromophore, bis(carboxy-ethyl)-carboxyfluorescein. Hepatocytes, after being acidified by an NH4Cl prepulse, exhibit amiloride-sensitive and sodium-dependent alkalinization. The rate of cellular pH recovery after acidification varied with the intracellular pH. The rate was highest at approximately pH 6.4 and declined as the pH rose, ceasing measurable activity at approximately pH 7.3. The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate, at a concentration of 10(-6) M, shifted the set point for the exchanger to a more alkaline pH by 0.2-0.3 pH units. The above observations indicate that the Na+-H+ exchanger plays an active role in regulating intracellular pH in liver cells and that hormones acting through protein kinase C may modulate that function.