Liu Qiang, Chen Bojun, Ge Qian, Wang Zhao-Wen
Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut 06030, USA.
J Neurosci. 2007 Sep 26;27(39):10404-13. doi: 10.1523/JNEUROSCI.5634-06.2007.
Although Ca2+/calmodulin-dependent protein kinase II (CaMKII) is enriched at the presynaptic nerve terminal, its role in neurotransmitter release is poorly defined. We assessed the function of presynaptic CaMKII in neurotransmitter release and tested the hypothesis that BK channel is a mediator of presynaptic CaMKII function by analyzing miniature and evoked postsynaptic currents at the Caenorhabditis elegans neuromuscular junction. Both loss-of-function (lf) and gain-of-function (gf) of unc-43, the gene encoding CaMKII, inhibited neurotransmitter release. The inhibitory effect of unc-43(gf) was reversed by mutation or blockade of the BK channel SLO-1. SLO-1 expressed in Xenopus oocytes could be activated by recombinant rat alpha-CaMKII, and this effect of CaMKII was abolished by mutating a threonine residue (T425) at a consensus CaMKII phosphorylation site in the first RCK (regulator of conductance for K+) domain of the channel. Expression of slo-1(T425A) in neurons antagonized the inhibitory effect of unc-43(gf) on neurotransmitter release as slo-1(lf) did. The inhibitory effect of unc-43(gf) was not reversed by unc-103(lf), dgk-1(lf), or eat-16(lf), which reportedly suppress behavioral phenotypes of unc-43(gf). These observations suggest that presynaptic CaMKII is a bidirectional modulator of neurotransmitter release, presumably by phosphorylating different molecular targets, and that its negative modulatory effect on the release is mainly mediated by SLO-1 activation.
尽管钙离子/钙调蛋白依赖性蛋白激酶II（CaMKII）在突触前神经末梢中含量丰富，但其在神经递质释放中的作用仍不清楚。我们评估了突触前CaMKII在神经递质释放中的功能，并通过分析秀丽隐杆线虫神经肌肉接头处的微小和诱发的突触后电流，检验了BK通道是突触前CaMKII功能的介导者这一假设。编码CaMKII的基因unc-43的功能丧失（lf）和功能获得（gf）均抑制了神经递质释放。BK通道SLO-1的突变或阻断可逆转unc-43（gf）的抑制作用。非洲爪蟾卵母细胞中表达的SLO-1可被重组大鼠α-CaMKII激活，而通道第一个RCK（钾离子电导调节剂）结构域中CaMKII磷酸化位点的苏氨酸残基（T425）发生突变后，CaMKII的这种作用就会消失。神经元中slo-1（T425A）的表达与slo-1（lf）一样，拮抗了unc-43（gf）对神经递质释放的抑制作用。unc-103（lf）、dgk-1（lf）或eat-16（lf）不能逆转unc-43（gf）的抑制作用，据报道这些基因可抑制unc-43（gf）的行为表型。这些观察结果表明，突触前CaMKII可能通过磷酸化不同的分子靶点，对神经递质释放起双向调节作用，并且其对释放的负向调节作用主要由SLO-1激活介导。
