A Comparison between Organomercurial- and Progesterone-Induced Maturation in Amphibian Oocytes

Abstract

From the many substances tested, only organomercurials which do not penetrate well into the cells (PHMB, PHMPS, meralluride, mersalyl), and cysteamine-induced maturation in Xenopus laevis oocytes. Organomercurials which easily penetrate into the cells are toxic. All thiols reverse the inducing effects of the organomercurials. Dithiothreitol (DTT), in contrast to monothiols, inhibits progesterone-induced maturation provided that it is added within the first 2–3 h of progesterone treatment. Repeated injections of PHMPS into Xenopus oocytes fail to induce maturation. Extensive cytological analysis and a study of the effects of cyanoketone have confirmed that the organomercurials act on the oocyte itself and not on the surrounding follicle cells. Organomercurials induce maturation in oocytes of Ambystoma mexicanum and Rana temporaria. Ouabain, but not other inhibitors of (Na+, K+) ATPase (ethacrynic acid, showdomycin, DTNB), accelerates progesterone-induced maturation. None of these inhibitors induces maturation by itself. Procain does not induce maturation and slows down progesterone-induced maturation. SITS inhibits organomercurial-, but not progesterone-induced maturation. Injection of protease inhibitors (TPCK, TLCK, pepstatin, leupeptin) into oocytes does not prevent GV breakdown. Stimulation of maturation by organomercurials increases the oxygen consumption of the treated oocytes. Binding of 203Hg labelled organomercurials follows biphasic kinetics. It is inhibited by SITS and accelerated by progesterone. ATPase activity is highest in melanosomes; it is barely stimulated by Na+ and K+ and is almost insensitive to ouabain. It is strongly stimulated by Ca2+ and traces of Mg2+. There are transitory increases in total ATPase activity 1 and 4 h after the induction of maturation.