Activation of protein kinase C potentiates norepinephrine release from sinus node.

Localization of binding sites of [20-3H]phorbol-12,13-dibutyrate [( 3H]PDBu) and the involvement of Ca2+-phospholipid-dependent protein kinase (protein kinase C) in the release of norepinephrine (NE) from sympathetic nerve terminals in the guinea pig sinus node were investigated. There was a single class of specific [3H]PDBu binding sites in the heart. [3H]NE release from the sinus node preloaded with [3H]NE was evoked by electrical stimulation in superfusing medium containing Ca2+ or by the concomitant presence of Ca2+ ionophore and Ca2+, in Ca2+-free medium. 12-O-tetradecanoylphorbol-13-acetate (TPA) potentiated the evoked [3H]NE release. The effect of TPA was antagonized by both polymyxin B and H-7, inhibitors of protein kinase C. TPA increased the apparent affinities of electrical stimulation-evoked release for extracellular Ca2+. The possibility that protein kinase C plays a role in transmembrane signal transduction involved in the release of NE from peripheral adrenergic nerve terminals in the guinea pig sinus node warrants continued study.