Involvement of GABAAreceptor inBufo arenarumoocyte maturation

Abstract

SummaryAmphibian oocytes meiotic arrest is released under the stimulus of progesterone; this hormone interacts with the oocyte surface and starts a cascade of events leading to the activation of a cytoplasmic maturation promoting factor (MPF) that induces germinal vesicle breakdown (GVBD), chromosome condensation and extrusion of the first polar body.The aim of this work was to determine whether the activation of a GABAAreceptor is able to induce GVBD in fully grown denuded oocytes ofBufo arenarumand to analyse its possible participation in progesterone-induced maturation. We also evaluated the role of purines and phospholipids in the maturation process induced by a GABAAreceptor agonist such as muscimol.Our results indicated that the activation of the GABAAreceptor by muscimol induces maturation in a dose- and time-dependent manner and that this activation is a genuine maturation that enables oocytes to form pronuclei. Assays with a receptor antagonist, picrotoxine, showed that the maturation induced by muscimol was inhibited. Treatment with picrotoxine, however, shows that the participation of GABAAreceptor in progesterone-induced maturation is not significant.In addition, our results indicate that high intracellular levels of purines obtained by the use of db-AMPc and theophylline or the inhibition of the phosphatidylinositol 4,5-bisphosphate (PIP2hydrolysis by neomycin and PIP2turn over by LiCl, respectively, inhibited the maturation induced by muscimol. Treatment with H-7 indicated, however, that PKC activation is not necessary for GVBD induced by the GABAAreceptor agonist. Results suggest that the transduction pathway used by the GABAAreceptor to induce maturation is different from those used by progesterone.