Relationship between intracellular pH and chloride in Xenopus oocytes expressing the chloride channel ClC-0

Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510 During maturation of oocytes, Cl conductance ( G Cl ) oscillates and intracellular pH (pH i ) increases. Elevating pH i permits the protein synthesis essential to maturation. To examine whether changes in G Cl and pH i are coupled, the Cl channel ClC-0 was heterologously expressed. Overexpressing ClC-0 elevates pH i , decreases intracellular Cl concentration ([Cl ] i ), and reduces volume. Acute acidification with butyrate does not activate acid extrusion in ClC-0-expressing or control oocytes. The ClC-0-induced pH i change increases after overnight incubation at extracellular pH 8.5 but is unaltered after incubation at extracellular pH 6.5. Membrane depolarization did not change pH i . In contrast, hyperpolarization elevates pH i . Thus neither membrane depolarization nor acute activation of acid extrusion accounts for the ClC-0-dependent alkalinization. Overnight incubation in low extracellular Cl concentration increases pH i and decreases [Cl ] i in control and ClC-0 expressing oocytes, with the effect greater in the latter. Incubation in hypotonic, low extracellular Cl solutions prevented pH i elevation, although the decrease in [Cl ] i persisted. Taken together, our observations suggest that KCl loss leads to oocyte shrinkage, which transiently activates acid extrusion. In conclusion, expressing ClC-0 in oocytes increases pH i and decreases [Cl ] i . These parameters are coupled via shrinkage activation of proton extrusion. Normal, cyclical changes of oocyte G Cl may exert an effect on pH i via shrinkage, thus inducing meiotic maturation. cell volume; acid extrusion; ion-sensitive microelectrodes