Cl(-)-HCO3- exchanger in isolated rat hepatocytes: role in regulation of intracellular pH

In rat hepatocytes, basolateral Na+-H+ exchange and Na+-HCO3- cotransport function as acid extruders. To assess mechanisms of acid loading, intracellular pH (pH(i)) recovery from an alkaline load was analyzed in short-term cultured rat hepatocyte monolayers using the pH-sensitive dye BCECF. Electrophysiological techniques were also used to assess the role of the membrane potential (V(m)). Cells were alkaline loaded by suddenly reducing external CO2 and HCO3- (from 10% and 50 mM, respectively, to 5% and 25 mM) at constant pH(o). After this maneuver, pH(i) rapidly rose by 0.13 ± 0.03 pH units (pH(u)) and recovered to baseline at an initial rate of 0.026 ± 0.009 pH(u))/min. Intracellular buffering power was estimated from the dependence of pH(i) on [NH4+](o) and varied between 70 and 10.5 mM/pH(u) in a pH(i) range of 6.5-7.6. Initial pH(i) recovery corresponded to a rate of OH- efflux (J(OH)) of 1.76 ± 0.71 mM/min and was blocked by 0.5 mM DIDS (0.003 ± 0.002; J(OH) = 0.18 ± 0.06) or by 1...