Enhancing effect of protein kinase C activation on high K(+)-induced norepinephrine release

Raising the concentration of K+ in the superfusion medium increased the release of [3H]norepinephrine ([3H]NE) from rabbit hippocampus slices preincubated with [3H]NE. This evoked [3H]NE release was modulated by presynaptic alpha 2-adrenergic, presynaptic opioid kappa- and A1-adenosine receptors and augmented with increasing K+ concentration (20-120 mmol.L-1). The enhancement or inhibition of this release by activator (phorbol ester) or inhibitor (polymyxin B) of protein kinase C was blocked by tetrodotoxin and reduced with increasing K+ concentration. It was suggested that the Na(+)-influx was involved in the protein kinase C effect on the K(+)-evoked [3H]NE release.