Suppression of spontaneous maturation of isolated cumulus-free mouse oocytes by a calmodulin antagonist

Oocytes isolated from antral follicles undergo spontaneous maturation when cultured in vitro. W7, a calmodulin antagonist, at concentration of more than 50 microM blocked the occurrence of spontaneous germinal vesicle breakdown (GVBD) in isolated cumulus-free mouse oocytes. The inhibition of maturation was observed in more than 90% of oocytes when W7 was added within 15 min after the initiation of incubation of the oocytes. The block was partially reversible. Hypoxanthine, estradiol-17 beta, testosterone and progesterone did not influence the inhibition induced with W7. The present results suggest that calmodulin is involved in the early stage of mouse oocyte maturation.