Induction of amphibian oocyte maturation by polyvalent cations and alkaline pH in the absence of potassium ions

Abstract

The maturation of Xenopus laevis oocytes was studied in media free of added potassium salts. Under these conditions maturation could be triggered by 1 m M Mn 2+ and La 3+ and, to a lesser extent, by 2–4 m M Ca 2+ and Mg 2+. Maturation induced by 1.5 m M Mn 2+ was inhibited by K + concentrations above 0.25 m M. Potassium was inhibitory when added up to 2 hr before germinal vesicle breakdown occurred. In potassium-free media, maturation could be induced by incubation of oocytes under mild alkaline media (pH 8.5–9). A high percentage of medium-sized oocytes (stage IV according to Dumont) was induced to mature by progesterone in the absence of potassium. Maturation of oocytes in potassium-free media was normal by the criteria of germinal vesicle breakdown, production of maturation promoting factor, vitelline membrane activation, and inhibition by known maturation inhibitors.