PROTEIN-KINASE-C AND THE REGULATION OF GLUTAMATE EXOCYTOSIS FROM CEREBROCORTICAL SYNAPTOSOMES

The role of protein kinase C (PKC) in the regulation of transmitter gl utamate release from rat cerebral cortical synaptosomes is investigate d. Two depolarization protocols are used: first, elevated KCl, which p roduces a clamped depolarization, and second, 4-aminopyridine, which e vokes spontaneous ''action potentials'' allowing any potential modulat ion of Na+ or K+ channels to influence release. Although the PKC inhib itor Ro 31-8220 prevents both the depolarization-evoked and phorbol di butyrate (PDBu)-evoked phosphorylation of the major presynaptic PKC su bstrate, myristoylated alanine-rich C kinase substrate, it is without effect on KCl-evoked Ca2+-dependent glutamate release. Ro 31-8220 tota lly inhibits the Ca2+-dependent 4-aminopyridine-evoked release of glut amate in the presence and absence of PDBu and again decreases the phos phorylation of myristoylated alanine-rich C kinase substrate. Ro 31-82 20 strongly inhibits the 4-aminopyridine-evoked increase in [Ca2+] bot h in the presence and absence of PDBu and antagonizes the PDBu enhance ment of depolarization. This indicates that PKC isoforms activatable b y PDBu and sensitive to Ro 31-8220 play no discernable role in Ca2+-se cretion coupling per se in cerebral cortical glutamatergic nerve termi nals, but that the kinase plays a major role in regulating the depolar ization of the terminal.