SELECTIVE ACTIVATION OF CA2+-ACTIVATED PKCS IN APLYSIA NEURONS BY 5-HT

Ca2+-activated and Ca2+-independent protein kinase Cs (PKCs) are present in the nervous system of the marine mollusk Aplysia californica (Kruger et al., 1991). Sensitizing stimuli or application of the facilitatory transmitter 5-HT to intact isolated ganglia produces the presynaptic facilitation of sensory-to-motor neuron synapses that underlies behavioral sensitization, which is a simple form of learning. Activation of PKC can also produce this presynaptic facilitation (Braha et al., 1990). To determine which type of PKC is activated, we developed a sensitive and selective assay to measure both Ca2+-activated and Ca2+-independent PKC activities in crude supernatant and membrane fractions of nervous tissue. This assay is based on the specific binding of the Ca2+-activated PKCs to phosphatidylserine vesicles in the presence of Ca2+ and makes use of a novel synthetic peptide with sequences conforming to phylogenetically conserved pseudosubstrate regions of the Ca2+-independent kinases. We provide evidence that the presynaptic facilitation is produced by a Ca2+-activated isoform: application of 5-HT increases the amount of the Ca2+-activated PKC activity associated with the membrane. Under these conditions, no increase in Ca2+-independent kinase activity is seen.