A single-cell approach for measuring the concentration of cytoplasmic calcium ions ([Ca2 ]i) and a protein kinase C-epsilon (PKCε)-specific inhibitor were used to investigate the developmental role of PKCε in the prostaglandin F2α(PGF2α)-induced rise in [Ca2 ]i and the induced decline in progesterone accumulation in cultures of cells isolated from the bovine corpus luteum. PGF2α increased [Ca2 ]i 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 PGF2α-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 PKCε inhibitor reduced the PGF2α-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. PGF2α inhibited LH-stimulated progesterone (P4) accumulation only in the incubation medium of Day 10 luteal cells. Both conventional and PKCε-specific inhibitors reversed the ability of PGF2α to decrease LH-stimulated P4 accumulation, and the PKCε inhibitor was more effective at this than the conventional PKC inhibitor. In conclusion, the evidence indicates that PKCε, an isozyme expressed in corpora lutea with acquired PGF2α luteolytic capacity, has a regulatory role in the PGF2α-induced Ca2 signaling in luteal steroidogenic cells, and that this in turn may have consequences (at least in part) on the ability of PGF2α to inhibit LH-stimulated P4 synthesis at this developmental stage.
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