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Effects of Selective Protein Kinase C Isozymes in Prostaglandin₂-Induced Ca²⁺ Signaling and Luteinizing Hormone-Induced Progesterone Accumulation in the Mid-Phase Bovine Corpus Luteum¹

Department of Biology,³ Eberly College of Arts and Sciences; Division of Animal and Veterinary Sciences,⁴ College of Agriculture, Forestry and Consumer Sciences, West Virginia University, Morgantown, West Virginia 26506

A single-cell approach for measuring the concentration of cytoplasmic calcium ions ([Ca²⁺]_i) and a protein kinase C-epsilon (PKC)-specific inhibitor were used to investigate the developmental role of PKC in the prostaglandin F₂(PGF₂)-induced rise in [Ca²⁺]_i and the induced decline in progesterone accumulation in cultures of cells isolated from the bovine corpus luteum. PGF₂ 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 PGF₂-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 inhibitor reduced the PGF₂-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. PGF₂ inhibited LH-stimulated progesterone (P₄) accumulation only in the incubation medium of Day 10 luteal cells. Both conventional and PKC-specific inhibitors reversed the ability of PGF₂ to decrease LH-stimulated P₄ accumulation, and the PKC inhibitor was more effective at this than the conventional PKC inhibitor. In conclusion, the evidence indicates that PKC, an isozyme expressed in corpora lutea with acquired PGF₂ luteolytic capacity, has a regulatory role in the PGF₂-induced Ca²⁺ signaling in luteal steroidogenic cells, and that this in turn may have consequences (at least in part) on the ability of PGF₂ to inhibit LH-stimulated P₄ synthesis at this developmental stage.

¹ Supported in part by a U.S. Department of Agriculture CREES award 2002-35203-12230 to E.K.I. and J.A.F.

² Correspondence: Jorge A. Flores, Department of Biology, Eberly College of Arts and Sciences, West Virginia University, P.O. Box 6057, Morgantown, WV 26506-6057. FAX: 304 293 6363; jflores{at}wvu.edu

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