Protein kinase Cδ mediates ethanol-induced up-regulation of L-type calcium channels

Abstract

Brief ethanol exposure inhibits L-type, voltage-gated calcium channels in neural cells, whereas chronic exposure increases the number of functional channels. In PC12 cells, this adaptive response is mediated by protein kinase C (PKC), but the PKC isozyme responsible is unknown. Since chronic ethanol exposure increases expression of PKCδ and PKCε, we investigated the role these isozymes play in up-regulation of L-type channels by ethanol. Incubation with the PKC inhibitor GF 109203X or expression of a PKCδ fragment that inhibits phorbol ester-induced PKCδ translocation largely prevented ethanol-induced increases in dihydropyridine binding and K+- stimulated 45Ca2+ uptake. A corresponding PKCε fragment had no effect on this response. These findings indicate that PKCδ mediates up-regulation of L-type channels by ethanol. Remaining responses to ethanol in cells expressing the PKCδ fragment were not inhibited by GF 109203X, indicating that PKCδ-independent mechanisms also contribute. PKCδ overexpression increased binding sites for dihydropyridine and L-channel antagonists, but did not increase K+-stimulated 45Ca2+ uptake, possibly because of homeostatic responses that maintain base-line levels of channel function. Since L-type channels modulate drinking behavior and contribute to neuronal hyperexcitability during alcohol withdrawal, these findings suggest an important role for PKCδ in alcohol consumption and dependence.