To investigate the regulation of free cytosolic calcium concentration ([Ca2+]i) by the adenosine 3′,5′-cyclic monophosphate (cAMP) signaling system in clonal gonadotrophs, microfluorimetric recordings were made in single indo 1-loaded αT3–1 cells. Forskolin, 8-bromoadenosine 3′,5′-cyclic monophosphate, or a low concentration (100 pM) of the hypothalamic factor pituitary adenylate cyclase-activating polypeptide (PACAP) stimulated Ca2+ step responses or repetitive Ca2+ transients, which were blocked by the removal of extracellular Ca2+ by the dihydropyridine (DHP) (+)PN 200–110 or by preincubation with the protein kinase A (PKA) antagonist H-89 (10 μM). Thus activation of the cAMP/PKA system in αT3–1 gonadotrophs stimulates Ca2+ influx through DHP-sensitive (L-type) Ca2+ channels. In contrast, high PACAP concentrations (100 nM) stimulated biphasic Ca2+ spike-plateau responses. The Ca2+ spike was independent of extracellular Ca2+, and similar responses were observed by microperfusion of individual cells withd- myo-inositol 1,4,5-trisphosphate, suggesting the involvement of the phospholipase C (PLC) signaling pathway. The Ca2+plateau depended on Ca2+ influx, was blocked by (+)PN 200–110, but was only partially blocked by H-89 pretreatment. In conclusion, PACAP stimulates [Ca2+]iincreases in αT3–1 gonadotrophs through both the PLC and adenylate cyclase signaling pathways. Furthermore, this is the first clear demonstration that the cAMP/PKA system can mediate changes in [Ca2+]iin gonadotroph-like cells.
MODULATION OF THE HYDROGEN PEROXIDE LEVEL AND COMPONENTS OF THE ADENYLATE CYCLASE SIGNALING SYSTEM IN ROOTS OF PEA SEEDLINGS DEPENDING ON THE EFFECTIVENESS OF RHIZOBIUM LEGUMINOSARUM BV. VICEAE STRAINS
