RECEPTION AND TRANSDUCTION OF THE SEROTONIN SIGNAL RESPONSIBLE FOR MEIOSIS REINITIATION IN OOCYTES OF THE JAPANESE CLAM RUDITAPES-PHILIPPINARUM

Prophase-arrested oocytes of Ruditapes philippinarum are triggered to undergo germinal vesicle breakdown under the influence of the neurohor mone serotonin (5HT) and then arrest in metaphase 1. Our data show tha t these oocytes possess a single class of original 5HT receptors. Thei r binding parameters have been determined on semipurified membrane pre parations incubated with [H-3]5HT. No significant differences were obs erved when comparing 5HT-competent and -incompetent batches as well as prophase- or metaphase-arrested oocytes. Specific experiments includi ng incubation with mastoparan or mas 7, GTP iontophoresis, and IP3 qua ntification strongly suggest that these receptors must be coupled with G-proteins to be functional. Peak change in IP3 mass occurs at 3 min and is likely to trigger the 5HT-dependent Ca2+ transient that begins at this time. In metaphase-arrested oocytes, binding of 5HT to its rec eptors no longer produces a Ca2+ surge. This is likely to result from a negative retrocontrol loop which would involve kinase C and exert it s effect upstream of the Ca2+ surge. Indeed, the phorbol ester PMA pro ved able to reduce the Ca2+ response and to block 5HT action when appl ied during the first 3 min corresponding to the hormone-dependent peri od. Such an inhibition was reversed in the presence of 5 mu M of the C kinase inhibitor GF109203X and could be bypassed by ionophore, ammoni a, and thapsigargin, which trigger a receptor-independent Ca2+ surge. (C) 1994 Academic Press, Inc.