Role of cyclic AMP-dependent protein kinase in oocyte maturation of the catfish, Clarias batrachus.

The results of the present study demonstrate the probable involvement of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase (PKA) in the regulation of oocyte maturation in the catfish, Clarias batrachus. A decrease in total PKA activity with a concomitant increase in the percentage of germinal vesicle breakdown (GVBD) was found in oocytes treated with different doses of N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinoline sulfonamide (H-89), a selective, potent inhibitor of PKA and 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17 alpha, 20 beta-DP), the natural maturation-inducing steroid of this catfish. Evaluation of time-course of response to H-89 and 17 alpha, 20 beta-DP revealed that PKA activity decreased, and incidence of GVBD increased at all the time points when compared with their respective controls. The data further indicate that the decrease in PKA activity in H-89-treated oocytes was more prominent, but the induction of maturation was slower than that induced by 17 alpha, 20 beta-DP. Moreover, cyanoketone (CK), an inhibitor of steroidogenesis that blocks the salmon gonadotropin (SG-G100)-induced GVBD, failed to abolish the maturational effect of H-89, suggesting that H-89 directly promotes GVBD by reducing PKA activity in oocytes. Taken together, these results indicate that inhibition of PKA activity in the oocyte of C. batrachus is directly involved in the mechanism leading to oocyte maturation. Copyright 2002 Wiley-Liss, Inc.