Is the calcium signal induced by follicle-stimulating hormone in swine granulosa cells mediated by adenosine cyclic 3',5'-monophosphate-dependent protein kinase?

Abstract

We have previously demonstrated FSH-induced increases in cytosolic free calcium ion concentrations ([Ca2+]i) in single granulosa cells. We report here on the role of cAMP-dependent protein kinase (PKA) in the FSH-induced [Ca2+]i increase using swine granulosa cells. The R-isomer of cAMP (Rp-cAMPS) and a synthetic peptide containing the active core region of the PKA inhibitor were used as specific inhibitors of PKA. The Rp-cAMPS dose used was effective in completely abolishing FSH-stimulated progesterone production by cultured granulosa cells. However, FSH retained its ability to initiate a calcium signal even in the presence of the cAMP antagonist. In addition, both Rp-cAMPS and the PKA inhibitor peptide significantly reduced the percentage of granulosa cells able to generate [Ca2+]i signals in response to 8-bromo-cAMP without affecting the percentage of [Ca2+]i responses to FSH. We conclude from these observations that at least two aspects, percentage of responding cells and kinetics of the response, of FSH-induced [Ca2+]i increases in swine granulosa cells appear to be independent of the action of PKA. Such findings suggest a direct action of cAMP on [Ca2+]i or cAMP-independent action(s) of FSH in granulosa cells.