Protein Kinase C Activators Enhance Transmission at the Squid Giant Synapse

¹ Section of Neurobiology, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-0371, Catalina Marine Science Center, P.O. Box 398, Avalon, California 90704, and Marine Biological Laboratory, Woods Hole, Massachusetts 02543
² Department of Physical Medicine and Rehabilitation, University of Michigan, Ann Arbor, Michigan 48109, Marine Biological Laboratory, Woods Hole, Massachusetts 02543

We have examined the possible role of protein kinase C in synaptic transmission by asking whether agents that activate protein kinase C affect transmission at the squid giant synapse. Several phorbol esters and a synthetic diacylglycerol that activates the kinase produced a substantial enhancement of transmission at the squid synapse, while structurally related compounds incapable of activating the kinase did not affect transmission. These agents enhanced both postsynaptic potentials and postsynaptic currents, revealing that they were not enhancing transmission exclusively by increasing postsynaptic input resistance. The increase in transmission produced by phorbol esters was either irreversible or reversed over a time course of one hour or longer. Kinase C activators also enhanced transmission at other synapses in the squid stellate ganglion. Our results are consistent with a general role for protein kinase C in synaptic transmission and indicate that the squid giant synapse is a favorable experimental system for further elucidation of the specific function of kinase C at synapses.