Enhanced spontaneous transmitter release at murine motor nerve terminals with cyclosporine.

Cyclosporine, a calcineurin inhibitor, significantly enhances spontaneous acetylcholine release after a brief tetanus and potentiates the effect of phorbol 12,13-dibutyrate. Both actions are prevented by the protein kinase C inhibitor, bisindolylmaleimide iodide. Protein kinase C and calcineurin thus play important roles in the balance between phosphorylation and dephosphorylation regulating spontaneous transmitter release at motor nerve terminals.