Phorbol ester and sperm activate mouse oocytes by inducing sustained oscillations in cell Ca2+

The parthenogenetic activation of mouse oocytes by several agents is accompanied by a large rise in the intracellular calcium concentration ( [Ca2+]i). The tumour-promoting phorbol ester 12-O-tetradecanoyl phorbol acetate (TPA) activates some cellular processes which are also activated by raised [Ca2+] (ref. 2). We therefore tested TPA on mouse oocytes and found it to be a potent parthenogenetic activating agent. Recent reports suggest that TPA mimics endogenous diacylglycerol3 and can stimulate cells by activating protein kinase C without raising [Ca2+]i (refs 4, 5). We have now measured [Ca2+]i with aequorin in mouse oocytes treated with TPA. Sustained oscillations in [Ca2+]i appeared in those oocytes which were subsequently activated. We also measured [Ca2+]i during fertilization. The response began with [Ca2+]i transients as reported previously, but the transients continued in a regular pattern for 4 h. There was no rise in [Ca2+]i of the type induced by activating agents such as ethanol. One component of the fertilization response appears to be related to the TPA-induced oscillations.