Preferential release of catecholamine from permeabilized PC12 cells by α- and β-type protein kinase C subspecies

Protein kinase C (PKC) is now recognized as comprising two groups of closely related subspecies. The PKCγ enzyme is apparently present only in central nervous tissues, and hence was expected to participate in neurotransmitter release. We have utilized a 'depletion-insertion' method to identify the PKCs participating in the exocytotic response. PC12 cells were 'down-regulated' by prior treatment (24h) with phorbol 12-myristate 13-acetate (PMA; 1μM), which nearly abolished endogenous PKC activity. Down-regulated PC12 cells were loaded with [³H]dopamine, permeabilized with digitonin, and recombinant or purified PKCs were inserted and activated with a low dose of PMA (20nM). Among group A PKCs, PKCα was the most effective activator of [³H] dopamine release (215%), followed by βII (185%) and βI (150%). PKCγ had no consistent effect on neurotransmitter release. PC12 cells express PKCα and PKCβ, but not PKCγ, as revealed by Northern-blot analysis. We therefore postulate that PKCα and PKCβ participate in neurotransmitter release, whereas PKCγ might be involved in other neuronal functions.