Protein kinase C activation in Aplysia neurons by phorbol diacetate: comparison of effects following extracellular or intracellular application.

The effects of protein kinase C activation on electrophysiological phenomena of neurons in Aplysia californica ganglions were studied. The enzyme was activated by phorbol-12,13-diacetate applied either extracellularly by perfusion, or by intracellular pressure injection. In both forms of application, an increase in the potential upstroke speed and amplitude as well as a reduction of the depolarization evoked by extracellular acetylcholine application was found. A protein kinase C blocker, H-7, had opposite effects on the action potential. All observed actions of the phorbol ester were consistently faster in intracellular application than extracellular.