Isoform‐specific inhibition of voltage‐sensitive Ca2+ channels by protein kinase C in adrenal chromaffin cells

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Abstract
Selective protein kinase C (PKC) activators and inhibitors were used to investigate the involvement of specific PKC isoforms in the modulation of voltage‐sensitive Ca2+ channels (VSCCs) in bovine adrenal chromaffin cells. Exposure to the phorbol ester phorbol‐12,13‐dibutyrate (PDBu) inhibited the Ca2+ currents elicited by depolarizing voltage steps. This inhibition was occluded by the PKC‐specific inhibitor Ro 31‐8220 but remained unaffected by Gö 6976, a selective inhibitor of conventional PKC isoforms. PDBu treatment caused the translocation of PKC‐α and ‐ϵ isoforms from cytosol to membranes. PKC‐ι and ‐ζ showed no signs of translocation. It is concluded that VSCCs are specifically inhibited by the activation of PKC‐ϵ in chromaffin cells. This may be relevant to the action of phospholipase‐linked receptors involved in the control of Ca2+ influx, both in catecholaminergic cells and other cell types.