THE RELATIONSHIP BETWEEN 3,5-CYCLIC ADENOSINE-MONOPHOSPHATE AND CALCIUM IN MEDIATING FOLLICLE-STIMULATING-HORMONE SIGNAL-TRANSDUCTION IN SERTOLI CELLS

FSH signal transduction in Sertoli cells involves the generation of cA MP and calcium as second messengers; however, the relationship between these two signals is not clear. In order to determine whether these w ere serial or parallel signals, we studied cytosolic calcium levels in freshly isolated rat Sertoli cells using maneuvers to dissociate gene ration of endogenous cAMP from cytosolic calcium. Pretreatment with 1 mM MDL 12,330A, an adenylate cyclase inhibitor, reduced by greater tha n 90% increases in cytosolic calcium induced by FSH (97 +/- 6 vs. 213 +/- 16 nM), whereas, despite adenylate cyclase blockade, 1 mM (Bu)(2)c AMP continued to elevate cytosolic calcium (from 87 +/- 6 to 182 +/- 2 3 nM), indicating the involvement of adenylate cyclase in the FSH-indu ced rise of cytosolic calcium. A cAMP antagonist, 1 mM R(p)-cAMP, redu ced by 75% the FSH-induced rise of cytosolic calcium (115 +/- 14 vs. 2 13 +/- 16 nM), suggesting that endogenous cAMP levels generated by FSH are sufficient to activate the cytosolic calcium response to FSH. Pre treatment with pertussis toxin (1 mg/liter) to dissociate the FSH-rece ptor interaction from its G-protein-mediated linkage to adenylate cycl ase also suppressed the FSH-induced rise in cytosolic calcium (97 +/- 11 vs. 213 +/- 16 nM). Sertoli cells preincubated with 1 mM staurospor ine, an inhibitor of protein kinases, exhibited a reduced calcium resp onse to FSH (125 +/- 14 vs. 213 +/- 16 nM), suggesting that FSH-induce d calcium flux might be mediated by protein kinase, presumably cAMP-de pendent protein kinase A. The present findings therefore strengthen th e premise that the cytosolic calcium response to FSH in Sertoli cells is predominantly attributable to serial signaling after the generation of endogenous cAMP.