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J. A. WEGNER, R. MARTINEZ-ZAGUILAN, R. J. GILLIES, P. B. HOYER, Prostaglandin F2α-lnduced Calcium Transient in Ovine Large Luteal Cells: II. Modulation of the Transient and Resting Cytosolic Free Calcium Alters Progesterone Secretion, Endocrinology, Volume 128, Issue 2, 1 February 1991, Pages 929–936, https://doi.org/10.1210/endo-128-2-929
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A previous study demonstrated that prostaglandin F2α (PGF2α stimulates a transient increase in cytosolic free Ca2+ levels ([Ca2+]i) in ovine large luteal cells. In the present study, the magnitude of the PGF2α (0.5 μM)-induced calcium transient in Hanks’ medium (87 ± 2 nM increase above resting levels) was reduced (P < 0.05) but not completely eliminated in fura-2 loaded large luteal cells incubated in Ca2+-free or phosphate- and carbonate-free medium (10 ± 1 nM, 32 ± 6 nM, above resting levels; respectively). Preincubation for 2 min with 1 mM LaCl3 (calcium antagonist) eliminated the PGF2α-induced calcium transient. The inhibitory effect of PGF2(, on secretion of progesterone was reduced in Ca2+-free medium or medium plus LaCU. Resting [Ca2+]i levels and basal secretion of progesterone were both reduced (P < 0.05) in large cells incubated in Ca2+- free medium (27 ± 4 nM; 70 ± 6% control, respectively) or with 5 μM 5,5′-dimethyl bis-(O-aminophenoxy)ethane-N,N,N’N’- tetraacetic acid (40 ± 2 nM; 49 ± 1% control; respectively). In addition, secretion of progesterone was inhibited (P < 0.05) by conditions that increased (P < 0.05) [Ca2+]i; that is LaCl3 ([Ca2+]i, 120 ± 17 nM; progesterone, 82 ± 8% control) and PGF2α ([Ca2+]i, 102 ± 10 nM; progesterone, 82 ± 3% control). In small luteal cells, resting [Ca2+]i levels and secretion of progesterone were reduced by incubation in Ca2+-free Hanks ([Ca2+]i, 28 ± 2 nM; progesterone, 71 ± 6% control), however, neither LaCl3 nor PGF2α increased [Ca2+]i levels or inhibited secretion of progesterone. The findings presented here provide evidence that extracellular as well as intracellular calcium contribute to the PGF2oinduced [Ca2+]i transient in large cells. Furthermore, whereas an adequate level of [Ca2+]i is required to support progesterone production in both small and large cells, optimal progesterone production in large cells depends upon an appropriate window of [Ca2+]i. (Endocrinology126: 929–936, 1991)
