Endocrinology, Vol 120, 853-859, Copyright © 1987 by Endocrine Society

ARTICLES

Luteinizing hormone-induced intracellular calcium mobilization in granulosa cells: comparison with forskolin and 8-bromo-adenosine 3',5'- monophosphate

EK Asem, M Molnar and F Hertelendy

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.