Effect of Ca2+-free Seawater Treatment on 1-Methyladenine Production in Starfish Ovarian Follicle Cells

When follicle cells from ovaries of the starfish Asterina pectinifera were washed with Ca²⁺-free seawater (CaFSW), the production of 1-methyladenine (1-MeAde) in response to gonad-stimulating substance (GSS) decreased to a large degree. The cyclic AMP content of CaFSW-treated follicle cells was much lower than that of non-treated cells, and the level was increased slightly by GSS, but not to a degree sufficient for production of 1-MeAde. The production of 1-MeAde and cyclic AMP in the presence of GSS was dependent on extracellular Ca²⁺ concentration, and was considerably reduced at a Ca²⁺ concentration below 1 mM. Thus, the decrease of 1-MeAde production by follicle cells after treatment with CaFSW is due to the low levels of cAMP. Furthermore, an ADP-ribosylation experiment using α-³²P]NAD⁺ in the presence of cholera toxin and pertussis toxin with membrane preparations of follicle cells treated with CaFSW revealed the presence of two types (stimulatory and inhibitory) of G-proteins. However, activity of the adenylyl cyclase was not influenced by GSS regardless of the presence or absence of GTP. These findings may suggest that GSS is unable to bind to its receptor in follicle cells after washing with CaFSW.