Prostaglandin F2 alpha-induced calcium transient in ovine large luteal cells: II. Modulation of the transient and resting cytosolic free calcium alters progesterone secretion.
A previous study demonstrated that prostaglandin F2 alpha (PGF2 alpha) stimulates a transient increase in cytosolic free Ca2+ levels [( Ca2+]i) in ovine large luteal cells. In the present study, the magnitude of the PGF2 alpha (0.5 microM)-induced calcium transient in Hanks' medium (87 +/- 2 nM increase above resting levels) was reduced (P less than 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 PGF2 alpha-induced calcium transient. The inhibitory effect of PGF2 alpha on secretion of progesterone was reduced in Ca2(+)-free medium or medium plus LaCl3. Resting [Ca2+]i levels and basal secretion of progesterone were both reduced (P less than 0.05) in large cells incubated in Ca2(+)-free medium (27 +/- 4 nM; 70 +/- 6% control, respectively) or with 5 microM 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 less than 0.05) by conditions that increased (P less than 0.05) [Ca2+]i; that is LaCl3 ([Ca2+]i, 120 +/- 17 nM; progesterone, 82 +/- 8% control) and PGF2 alpha ([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 PGF2 alpha 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 PGF2 alpha-induced [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.
Wegner
J A
JA
Department of Physiology, University of Arizona, Tucson 85724.
Martinez-Zaguilan
R
R
Gillies
R J
RJ
Hoyer
P B
PB
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003338:Corpus Luteum / Q000166:cytology / Q000378:metabolism*; D003470:Culture Media; D003600:Cytosol / Q000378:metabolism*; D015237:Dinoprost / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology / Q000031:analogs & derivatives; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D007811:Lanthanum / Q000494:pharmacology; D011374:Progesterone / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012146:Rest; D012756:Sheep
D003470:Culture Media; C028521:lanthanum chloride; D011374:Progesterone; D004533:Egtazic Acid; D007811:Lanthanum; C058180:5,5'-dimethyl-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate; D015237:Dinoprost; D002118:Calcium