Role of calcium in the modulation of ornithine decarboxylase activity in isolated pig granulosa cells in vitro.
We examined the role of Ca(2+) in the control of basal and hormone-stimulated ornithine decarboxylase activity in isolated pig granulosa cells maintained under chemically defined conditions in vitro. Omission of Ca(2+) from the incubation medium (measured Ca(2+) concentration 5mum) decreased basal enzymic activity, and significantly (P<0.01) impaired the response to maximally stimulating doses of either lutropin or follitropin. No significant alteration occurred in the concentration of either gonadotropin required to elicit half-maximal effects. The addition of EGTA (1.27-2.0mm) to chelate residual extracellular Ca(2+) further decreased hormone-induced rises in ornithine decarboxylase activity. Despite the presence of 1.27mm concentrations of extracellular Ca(2+), the administration of presumptive Ca(2+) antagonists, believed to impair trans-membrane Ca(2+) influx [verapamil (10-100mum), nifedipine (1-100mum) or CoCl(2) (1mm)] suppressed hormone-stimulated ornithine decarboxylase activity. The inhibitory effects of verapamil or of Ca(2+) omission from the medium were not overcome by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (0.25mm), or by cholera toxin, or by an exogenously supplied cyclic AMP analogue, 8-bromo cyclic AMP. Conversely, micromolar concentrations of a putative bivalent-cation ionophore, A23187, increased significantly the stimulation of ornithine decarboxylase activity by saturating concentrations of lutropin or 8-bromo cyclic AMP. Thus the present observations implicate Ca(2+) ions in the modulation of hormone action and cellular function in normal ovarian cells.
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002262:Carboxy-Lyases / Q000378:metabolism*; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D006107:Granulosa Cells / Q000187:drug effects / Q000201:enzymology*; D066298:In Vitro Techniques; D007986:Luteinizing Hormone / Q000494:pharmacology; D009955:Ornithine Decarboxylase / Q000378:metabolism*; D065108:Ornithine Decarboxylase Inhibitors; D013552:Swine; D014700:Verapamil / Q000494:pharmacology
D065108:Ornithine Decarboxylase Inhibitors; D015124:8-Bromo Cyclic Adenosine Monophosphate; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D014700:Verapamil; D000242:Cyclic AMP; D002262:Carboxy-Lyases; D009955:Ornithine Decarboxylase; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine