Inhibition of Na-alanine cotransport in oocytes of Xenopus laevis during meiotic maturation is voltage-regulated.

During progesterone-induced maturation of oocytes of Xenopus laevis the fast decrease of the rate of Na+-alanine cotransport is accompanied by a depolarization of the membrane potential and an increase in the intracellular Na+ activity. It is demonstrated that the decrease of the Na+-dependent alanine uptake is the result of the depolarization while the simultaneous increase in intracellular Na+ activity has no significant effect.