AN EARLY INCREASE IN CGMP FOLLOWS FERTILIZATION OF SEA-URCHIN EGGS

It has been proposed that both inositol trisphosphate and ryanodine re ceptors contribute to the Ca signal generated at fertilization of the sea urchin egg. Pharmacological studies indicate that cyclic adenosine diphosphate-ribose (cADPr) is the endogenous modulator of Ca release by the ryanodine-like receptor in eggs and that cADPR cyclase, the enz yme responsible for cADPR synthesis, can be stimulated by 3',5'-cyclic guanosine monophosphate (cGMP). Also, recent results show that the ga seous transmitter nitric oxide (NO) releases calcium in eggs via a mec hanism linked to cGMP and cADPR production. Results reported here show that fertilization induces a rapid and transient increase in the intr acellular concentration of cGMP. This increase occurs during the laten t period, before the major increase in cytoplasmic free calcium (Ca-i) , consistent with the hypothesis that cGMP production may play a key r ole in the Ca signal seen at fertilization. (C) 1996 Academic Press, I nc.