MODULATION OF SEROTONIN BINDING-SITES IN SPISULA-SOLIDISSIMA OOCYTES BY PHORBOL ESTER

In Spisula solidissima oocytes, serotonin (5-hydroxytryptamine, 5-HT)- dependent meiosis reinitiation is mediated via specific 5-HT membrane binding sites. This oocyte response is inhibited by the phorbol ester TPA. To assess whether the inhibitory effect of TPA was due to alterat ion of oocyte membrane binding sites, we studied their characteristics after TPA treatment. [H-3]-5HT binding assays revealed that TPA decre ased the affinity and, after prolonged treatment, increased the number of oocyte binding sites. Moreover, inhibitory actions of TPA on 5-HT- induced meiosis reinitiation paralleled its inhibitory effects on 5-HT binding site affinity. The inhibitory actions in biological assays we re restricted to TPA (an inactive analog of TPA, TPA-met was inefficie nt) and were completely reversed by staurosporine. Our data thus sugge st an inhibitory role for protein kinase C on oocyte 5-HT binding site s under physiological conditions.