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+]iincrease 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 completly 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+]isignals in response to 8-bromo-cAMP without affecting the percentage of [Ca2+]iresponses 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+]iincreases in swine granulosa cells appear to be independent of the action of PKA. Such findings suggest a direct action of cAMP on [Ca2+]ior cAMP-independent action(s) of FSH in granulosa cells.
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