PROSTAGLANDIN-F2-ALPHA RELEASES CALCIUM FROM A THAPSIGARGIN-SENSITIVE POOL IN OVINE LARGE LUTEAL CELLS

Thapsigargin (TG) and A23187 were used to examine the regulation of cytosolic free calcium (Ca-i(2+)) in ovine large and small luteal cells. Thapsigargin (50 nM) induced a sustained increase of Ca-i(2+) in fura 2-acetoxymethyl ester (AM)-loaded cells (large = 1.32 +/- 0.07-fold, small = 1.45 +/- 0.07-fold, P < 0.05). A23187 (1 mu M) induced a rapid transient increase of Ca-i(2+) (large = 1.37 +/- 0.07-fold, small = 1.46 +/- 0.10-fold, P < 0.05). In large cells, 0.5 mu M prostaglandin F-2 alpha (PGF(2 alpha)) increased Ca-i(2+) 1.54 +/- 0.11-fold. Pretreatment with 50 nM TG abolished the PGF(2 alpha)-induced calcium response. Pretreatment with PGF(2 alpha) attenuated (P < 0.05) the TG-induced Ca-i(2+) increase. Progesterone secretion was significantly (P < 0.05) inhibited by incubation with 50 nM TG, 1 mu M A23187, and 0.5 mu M PGF(2 alpha) in large but not small cells. These data suggest that PGF(2 alpha) releases calcium from a TG-sensitive intracellular calcium pool in ovine large luteal cells.