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Biol Reprod 1989 Jun;40(6):1144-1151
Department of Obstetrics and Gynecology, St. Louis University School of Medicine, Missouri 63104.
Previous studies in this laboratory have shown a remarkable increase in the capacity of avian granulosa cells to produce progesterone during the last 2-3 days of folliculogenesis, with concomitant increases in the activities of key steroidogenic enzymes. In view of the proposed involvement of inositol phospholipids and their hydrolytic products in signal transduction in steroidogenic cells, we investigated in this study the influence of follicular maturation on phosphoinositide-specific phospholipase C (PLC) and intracellular Ca2+ release in chicken granulosa cells. Resting concentrations of intracellular calcium ([Ca2+]i) as measured in Fura 2/AM-loaded cells increased significantly during the last 48 h of follicular maturation, from 185 +/- 9 nM in the third largest follicle (F3) to 355 +/- 26 in the cells of the largest (F1) follicle. Luteinizing hormone (LH) caused a dose-related rise in [Ca2+]i, but the dose response was left-shifted by more than one order of magnitude in F1 cells compared to F2 cells. In granulosa cells of less developed follicles, LH failed to raise [Ca2+]i. To assess PLC activity, granulosa cells from F1, F2, and F3 follicles were labeled with [3H]inositol for 2 h and then stimulated with LH (0.1 microgram/ml). Time course studies showed that within 30 s, phosphatidylinositol-4,5 bisphosphate (PIP2) decreased by 33%, 13%, and 11% in F1, F2, and F3 cells, respectively. Similar responses were obtained when permeabilized cells were exposed to guanosine 5'-O-thiotriphosphate, which also caused a corresponding increase in 45Ca efflux from F1 and F2 cells.
PMID: 2550086, UI: 89375551
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