Adrenergic regulation of translocation of protein kinase C isozymes in rat pinealocytes.

Protein kinase C (PKC) is involved in the alpha1-adrenergic-potentiation of beta-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 alpha (a classical PKC isozyme), PKC delta and epsilon (novel PKC isozymes), and PKC zeta: (atypical PKC isozymes). NE caused an increase in PKC alpha, delta, and epsilon, but not PKC zeta, in the particulate fraction. BAPTA-AM, which clamps intracellular Ca2+, reduced NE mediated translocation of PKC alpha, delta, and epsilon. Subjecting the animals to stimulus deprivation, which altered adrenergic-stimulated cyclic nucleotide responses, had no effect on the expression of PKC alpha, delta, epsilon, and zeta. Overnight treatment with 4beta-phorbol 12-myristate 13-acetate, an activator of PKC, down-regulated PKC alpha, delta, and epsilon, but not PKC zeta. Our results indicate that all three classes of PKC isozymes (PKC alpha, delta, epsilon, and zeta 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.