Luteinizing hormone-induced intracellular calcium mobilization in granulosa cells: comparison with forskolin and 8-bromo-adenosine 3',5'-monophosphate.
Digitonin-permeabilized avian granulosa cells were used as a model to study the effects of LH, 8-bromo-cAMP (8-Br-cAMP), and forskolin on intracellular calcium mobilization. LH caused a biphasic calcium efflux. There was a small but significant (P less than 0.05) calcium release within 1-2 min (rapid phase) with an ED50 of 35 ng/ml, followed by a larger one after 5 min (slow phase) with an ED50 of 10 ng/ml. The intracellular calcium antagonist TMB-8 inhibited the action of LH in both phases. Forskolin had no effect on calcium efflux during the rapid phase. However, it stimulated intracellular calcium efflux in a dose-dependent manner in the slow phase with an ED50 of 30 microM. Low doses of 8-Br-cAMP caused a small but significant increase in calcium uptake corresponding to the rapid phase, although high concentrations of 8-Br-cAMP caused efflux in the slow phase (ED50, 0.7 mM). Both LH and 8-Br-cAMP mobilized calcium from a nonmitochondrial pool, whereas forskolin induced calcium efflux from a nonendoplasmic reticular site. Apparently receptor-mediated (LH) and nonreceptor-mediated (forskolin and 8-Br-cAMP) intracellular calcium mobilization are qualitatively different, suggesting that rapid intracellular calcium mobilization may represent one of the initial steps in the mechanism of action of LH.
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002645:Chickens; D005576:Colforsin / Q000494:pharmacology*; D005260:Female; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D007986:Luteinizing Hormone / Q000494:pharmacology*
D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D007986:Luteinizing Hormone; D002118:Calcium