Mechanisms underlying endothelin's inhibition of FSH-stimulated progesterone production by ovarian granulosa cells

Protein kinase C (PKC) is involved in the ₁-adrenergic-potentiation of β-adrenergic stimulated cyclic nucleotide responses in rat pinealocytes. In the present study, the PKC isozymes expressed in rat pinealocytes and their regulation by norepinephrine (NE) were investigated. Western blot analysis identified PKC (a classical PKC isozyme), PKCδ and (novel PKC isozymes), and PKCζ: (atypical PKC isozymes). NE caused an increase in PKC, δ, and , but not PKCζ, in the particulate fraction. BAPTA-AM, which clamps intracellular Ca²⁺, reduced NE mediated translocation of PKC, δ, and . Subjecting the animals to stimulus deprivation, which altered adrenergic-stimulated cyclic nucleotide responses, had no effect on the expression of PKC, δ, , and ζ. Overnight treatment with 4β-phorbol 12-myristate 13-acetate, an activator of PKC, down-regulated PKC, δ, and , but not PKCζ. Our results indicate that all three classes of PKC isozymes (PKC, δ, , and ζ are expressed in the rat pineal gland. However, selective activation of these PKC isozymes does not appear to account for the differences in the pineal cAMP and cGMP responses to stimulation.