An autonomous kinase generated during long-term facilitation in Aplysia is related to the Ca(2+)-independent protein kinase C Apl II.

Prolonged treatment with serotonin leads to long-term facilitation of sensory-to-motor neuron synapses in Aplysia. We have shown previously that there is a protein synthesis-dependent increase in an autonomous kinase activity that phosphorylates a protein kinase C substrate during an intermediate phase of this facilitation. Here, I report that the increase in autonomous activity was independent of RNA synthesis, suggesting it may play a role in the maintenance phase of synaptic facilitation. Immunoprecipitation experiments using an antibody specific to the Ca(2+)-independent protein kinase C, Apl II, demonstrated that the autonomous kinase activity increased by serotonin emanated from Apl II. Chelerythrine, an inhibitor targeted to the substrate binding site of protein kinase C, also blocked the autonomous kinase activity increased by serotonin. Using immunoblotting experiments and calphostin-C, an inhibitor targeted to the regulatory domain of protein kinase C, the autonomous activity is shown not to be a catalytic fragment of Apl II. Furthermore, a higher concentration of calphostin-C was required to inhibit autonomous kinase activity than regulated kinase activity, suggesting that calphostin-C's binding site in the regulatory domain of Apl II is modified in the autonomous kinase. These data suggest that an autonomous kinase derived from Apl II may play a role in synaptic facilitation in Aplysia.