Protein kinase C modulates field-evoked transmitter release from cultured rat cerebellar granule cells via a dendrotoxin-sensitive K+ channel

The role of protein kinase C (PKC) in the control of neurotransmitter release from cultured rat cerebellar granule cells was investigated. Release of preloaded ³H]-d -aspartate which is incorporated into synaptic vesicles in this preparation was evoked by electrical field stimulation or elevated KCl. PKC activation by phorbol esters resulted in a large facilitation of field-evoked Ca²⁺-dependent ³H]-d -aspartate release and a lesser enhancement of KCl-stimulated release. Inhibition of PKC by Ro 31-8220 or staurosporine virtually abolished field-evoked release but had no effect on KCl-evoked release. Field-evoked, but not KCl-evoked, synaptic vesicle exocytosis monitored by the fluorescent vesicle probe FM2-10 was inhibited by staurosporine. PKC was not directly modulating neurite Ca²⁺ channels coupled to release, as Ro 31-8220 did not inhibit these channels. Activation or inhibition of PKC modulated field-evoked plasma membrane depolarization, but had no effect on KCl-evoked depolarization, consistent with a regulation of Na⁺ or K⁺ channels activated by field stimulation. No modulation of field-evoked neurite Na⁺ influx was seen using phorbol esters. Phorbol ester-induced facilitation of field-evoked ³H]-d -aspartate release and neurite Ca²⁺ entry was non-additive with that produced by the specific K⁺ channel antagonist dendrotoxin-1, suggesting that PKC modulates transmitter release from field-stimulated cerebellar granule cells by inhibiting a dendrotoxin-1-sensitive K⁺ channel.