TRANSLOCATION OF PROTEIN-KINASE CS IN APLYSIA NEURONS - EVIDENCE FOR COMPLEX REGULATION

We examined the activation of protein kinase C (PKC) produced by phorb ol esters in Aplysia nervous tissue. Translocation of PRC in intact ga nglia requires higher concentrations of phorbol esters than would be e xpected from: (1) their affinity for Aplysia PKCs measured in vitro; ( 2) their physiological effects on cultured Aplysia neurons; and (3) th eir actions on PKC in synaptosomes. Although phorbol esters enter inta ct ganglia slowly, delayed access to neurons is insufficient to accoun t for the high concentrations needed for translocation. Increasing acc essibility to the neural components of ganglia increases the rate at w hich translocation occurs, but does not affect the concentration of ph orbol ester required. We suggest that this might best be explained by the presence of a competitive inhibitor at the binding site for phorbo l esters in PKC. An indication for an inhibitor is that the concentrat ion of phorbol esters needed for translocation in homogenates of nervo us tissue is markedly decreased by diluting the extract. Preliminary c haracterization shows that the inhibitory activity is unusual: in addi tion to being competitive with lipid activators, it is soluble and tis sue-specific. This type of inhibitor may be an important regulator of protein phosphorylation by PKC in neurons.