Involvement of protein kinase C in the presynaptic nicotinic modulation of [H-3]-dopamine release from rat striatal synaptosomes

1 Presynaptic nicotinic ACh receptors modulate transmitter release in the brain. Here we report their interactions with protein kinase C (PKC) with respect to [H-3]-dopamine release from rat striatal synaptosomes, monitored by superfusion.
2 Two specific PKC inhibitors, Ro 31-8220 (1 muM) and D-erythro-sphingosine (10 muM) significantly reduced (by 51 and 26% respectively) [H-3]-dopamine release stimulated by anatoxin-a (AnTx), a potent and selective agonist of nicotinic ACh receptors. The inactive structural analogue of Ro 31-8220, bisindolylmaleimide V (1 muM) had no effect.
3 Two phorbol esters, PDBu (1 muM) and PMA (1 muM) potentiated AnTx-evoked [H-3]-dopamine release by 50-80%. This was Ca2+-dependent and prevented by PKC inhibitors. In the absence of nicotinic agonist, phorbol esters enhanced basal release through a PKC-independent mechanism.
4 A Rb-86(+) efflux assay of nicotinic ACh receptor function confirmed that Ro 31-8220 has no nonspecific effect on presynaptic nicotinic ACh receptors.
5 These results suggest that PKC is activated by nicotinic ACh receptor stimulation and mediates a component of AnTx-evoked [H-3]-dopamine release. In addition, independent activation of PKC can further amplify the response, offering a potential mechanism for receptor crosstalk.