The novel protein kinase C epsilon isoform modulates acetylcholine release in the rat neuromuscular junction

Background: Various protein kinase C (PKC) isoforms contribute to the phosphorylating activity that modulates neurotransmitter release. In previous studies we showed that nPKC epsilon is confined in the presynaptic site of the neuromuscular junction and its presynaptic function is activity-dependent. Furthermore, nPKC epsilon regulates phorbol ester-induced acetylcholine release potentiation, which further indicates that nPKC epsilon is involved in neurotransmission. The present study is designed to examine the nPKC epsilon involvement in transmitter release at the neuromuscular junction. Results: We use the specific nPKC epsilon translocation inhibitor peptide eV1-2 and electrophysiological experiments to investigate the involvement of this isoform in acetylcholine release. We observed that nPKC epsilon membrane translocation is key to the synaptic potentiation of NMJ, being involved in several conditions that upregulate PKC isoforms coupling to acetylcholine (ACh) release (incubation with high Ca2+, stimulation with phorbol esters and protein kinase A, stimulation with adenosine 3', 5'-cyclic monophosphorothioate, 8-Bromo-, Rp-isomer, sodium salt -Sp-8-BrcAMP-). In all these conditions, preincubation with the nPKC epsilon translocation inhibitor peptide (eV1-2) impairs PKC coupling to acetylcholine release potentiation. In addition, the inhibition of nPKC epsilon translocation and therefore its activity impedes that presynaptic muscarinic autoreceptors and adenosine autoreceptors modulate transmitter secretion. Conclusions: Together, these results point to the importance of nPKC epsilon isoform in the control of acetylcholine release in the neuromuscular junction.