Effects of selective protein kinase C isozymes in prostaglandin2α-induced Ca2+ signaling and luteinizing hormone-induced progesterone accumulation in the mid-phase bovine corpus luteum

A single-cell approach for measuring the concentration of cytoplasmic calcium ions ([Ca2+](i)) and a protein kinase C-epsilon (PKC epsilon)-specific inhibitor were used to investigate the developmental role of PKC epsilon in the prostaglandin F-2 alpha(PGF(2 alpha))-induced rise in [Ca2+]; and the induced decline in progesterone accumulation in cultures of cells isolated from the bovine corpus luteum. PGF(2 alpha) increased [Ca2+]; in Day 4 large luteal cells (LLCs), but the response was significantly lower than in Day 10 LLCs (4.3 +/- 0.6, n = 116 vs. 21.3 +/- 2.3, n = 110). Similarly, the fold increase in the PGF(2 alpha)-induced rise in [Ca2+](i) in Day 4 small luteal cells (SLCs) was lower than in Day 10 SLCs (1.6 +/- 0.2, n = 198 vs. 2.7 +/- 0.1, n = 95). A PKC epsilon inhibitor reduced the PGF2 alpha-elicited calcium responses in both Day 10 LLCs and SLCs to 3.5 +/- 0.3 (n = 217) and 1.3 +/- 0.1 (n = 205), respectively. PGF(2 alpha) inhibited LH-stimulated progesterone (P-4) accumulation only in the incubation medium of Day 10 luteal cells. Both conventional and PKC epsilon-specific inhibitors reversed the ability of PGF(2 alpha) to decrease LH-stimulated P-4 accumulation, and the PKC epsilon inhibitor was more effective at this than the conventional PKC inhibitor. In conclusion, the evidence indicates that PKC epsilon, an isozyme expressed in corpora lutea with acquired PGF(2 alpha) luteolytic capacity, has a regulatory role in the PGF(2 alpha)-induced Ca2+ signaling in luteal steroidogenic cells, and that this in turn may have consequences (at least in part) on the ability of PGF(2 alpha) to inhibit LH-stimulated P-4 synthesis at this developmental stage.