Multidirectional Effects of Calmodulin Kinase II on Transmitter Release in Mature and Newly Formed Mouse Motor Synapses

Calmodulin inhibitor W-7 did not cause changes in the quantal content of postsynaptic endplate potentials (EPP) in newly formed synapses, but prevented facilitation of acetylcholine secretion induced by L-type Ca2+ channels blocker nitrendipine. CaMKII inhibitor KN-62 produced similar effect and suppressed the increase in EPP quantal content caused by blockade of L-type Ca2+ channels. Phosphatase PP2A inhibitor okadaic acid significantly facilitated secretion in newly formed synapses; the effect was completely blocked by KN-62. In mature synapses, okadaic acid had no effect on transmitter secretion. KN-62 increased EPP quantal content. We hypothesize that CaMKII produced different effects on acetylcholine secretion in mature and immature synapses depending on specificity of calcium signaling and PP2A phosphatase activity.