Abstract

We have previously shown that short-term exposure to ethanol stimulates immunoreactive β-endorphin (IR-β-EP) release from hypothalamic neurons and that chronic ethanol exposure decreases the IR-β-EP release from these neurons. The role of protein kinase C (PKC) in the ethanol-regulated β-EP release from hypothalamic neurons has not been established. In this study, by using the primary cultures of hypothalamic neurons, we tested the effects of PKC stimulator phorbol ester 4β-phorbol 12-myristate-13-acetate (PMA) and PKC inhibitor chelerythrine chloride on ethanol-induced IR-β-EP release. Additionally, the effects of ethanol with or without PMA on expression and translocation of various PKC isoenzymes from cytosolic to membrane fraction were determined. PMA treatment increased IR-β-EP release in a time- and dose-dependent manner. Acute ethanol treatment (3 h) increased, while chronic ethanol treatment (24 h) reduced, the magnitude of PMA-induced IR-β-EP release. The stimulatory effect of acute ethanol on IR-β-EP release was reduced by chelerythrine chloride. Determination of the effects of ethanol with or without PMA on seven different PKC isoenzymes (PKC-α, -βI, -βII, -γ, -δ, -ε, and -ζ) revealed that the expression and translocation of only two PKC isoenzymes, PKC-δ and PKC-ε, were stimulated by acute treatment with ethanol. Acute ethanol also increased PMA-stimulated expression of these two isoenzymes. Chronic ethanol treatment reduced both basal and PMA-induced increase of PKC-δ and PKC-ε expression and translocation. These data provide evidence for the first time that ethanol-regulated IR-β-EP secretion is controlled by the PKC system, possibly involving PKC-δ and PKC-ε isoenzymes.