Ca(2+)-induced cortisol secretion from permeabilized bovine adrenocortical cells: the roles of calmodulin, protein kinase C and cyclic AMP.
In order to clarify the role of intracellular second messenger systems in the cortisol secretion from bovine adrenocortical (BAC) cells, the cells were permeabilized with beta-escin and stimulated intracellularly with various compounds. When the permeabilized BAC cells were exposed to submicromolar concentrations of Ca2+, a prompt cortisol secretion was elicited in a concentration-dependent manner. As the cells were stimulated with 12-O-tetradecanoyl-phorbol-13-acetate and 1-oleoyl-2-acetyl-glycerol, slow but persistent cortisol secretion was elicited, but in the case of 4 alpha-phorbol-12,13-didecanoate, no such effect was observed. The Ca(2+)-induced cortisol secretion was inhibited by simultaneous applications of calmodulin and protein kinase C (C kinase) inhibitors, but no significant inhibition was elicited by protein kinase A (A kinase) inhibitor. The results seem to indicate that in the Ca(2+)-induced cortisol secretion calmodulin may stimulate the initial stage, while C kinase may be involved mainly in the late phase of the secretion. In addition, cyclic AMP (cAMP) was also effective in activating cortisol secretion from permeabilized BAC cells. The cAMP-induced cortisol secretion was suppressed by an A kinase inhibitor but not affected by calmodulin or C kinase inhibitor. When Ca2+ and cAMP were added simultaneously at concentrations lower than those required to induce the cortisol secretion separately, a marked cortisol secretion was elicited, suggesting that a synergic action exists between Ca(2+)- and cAMP-activated systems. The Ca(2+)-induced cortisol secretion was suppressed by ruthenium red, an inhibitor of Ca2+ transport in the mitochondria. Although both NADP+ and NADPH elicited only a transient cortisol secretion, simultaneous addition of Ca2+ with NADP+ or NADPH caused a potent and sustained cortisol secretion. The augmentation due to Ca2+ on the NADP+ (or NADPH)-induced cortisol secretion was inhibited by the addition of a calmodulin inhibitor or a C kinase inhibitor, but not such effect was caused by A kinase inhibitor. From the present investigation, it was concluded that the Ca(2+)-dependent intracellular signal transduction may simulate the cortisol synthesis systems in the mitochondria of BAC cells.
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Okayama University, Japan.
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Yoshida
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Mio
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Tasaka
D000302:Adrenal Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology* / Q000502:physiology; D002147:Calmodulin / Q000494:pharmacology* / Q000502:physiology; D002417:Cattle; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000494:pharmacology* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D006854:Hydrocortisone / Q000378:metabolism*; D011493:Protein Kinase C / Q000494:pharmacology* / Q000502:physiology; D015290:Second Messenger Systems / Q000502:physiology*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002147:Calmodulin; D000242:Cyclic AMP; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D006854:Hydrocortisone