Presynaptic Ca²⁺/Calmodulin-Dependent Protein Kinase II Modulates Neurotransmitter Release by Activating BK Channels atCaenorhabditis elegansNeuromuscular Junction

Abstract

Although Ca2ϩ /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 ␣-CaMKII, and this effect of CaMKII was abolished by mutating a threonine residue (T 425 ) at a consensus CaMKII phosphorylation site in the first RCK (regulator of conductance for K ϩ ) domain of the channel. Expression of slo-1(T 425 A) 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.

Cell Excitability Necessary for Male Mating Behavior inCaenorhabditis elegansIs Coordinated by Interactions Between Big Current and Ether-A-Go-Go Family K+ Channels

“…slo-1 loss-offunction mutants exhibit many phenotypes, including impaired movement caused by defective neurotransmitter release, alcohol resistance, and muscle degeneration (Wang et al 2001;Davies et al 2003;Carre-Pierrat et al 2006;Liu et al 2007a). We found that 70% of males with an early nonsense mutation in slo-1 [allele js379, hereafter referred to as slo-1(lf); Wang et al 2001] spontaneously protract their spicules in the absence of mating cues (Table 1), demonstrating that like EAG and ERG-like K + channels, the BK channel also controls the excitability of male sex circuit components.…”

“…slo-1 has been shown in C. elegans and other systems to interact with calcium/calmodulin-dependent protein kinase II (CaMKII) (Hawasli et al 2004;Liu et al 2006Liu et al , 2007aLeBoeuf et al 2007). unc-43 encodes CaMKII in C. elegans and regulates movement, defecation, and egg laying in addition to its role in male mating (Reiner et al 1999).…”

Alternatively spliced domains interact to regulate BK potassium channel gating

“…In C. elegans, as in mammals, BK channels are widely expressed in both nerve and muscle (7,35) and regulate excitability in both tissues (7,36,37). Whereas slo-1 mutants establish the importance of BK channels for C. elegans physiology, they provide little insight into the contribution of alternative splicing.…”

Recruitment of sphingosine kinase to presynaptic terminals by a conserved muscarinic signaling pathway promotes neurotransmitter release

“…7B; Supplemental Table S3) ACh secretion Weimer et al 2003;Madison et al 2005;Gracheva et al 2006;Vashlishan et al 2008;Hobson et al 2011;Martin et al 2011). In contrast, mutants expressing a constitutively active slo-1/BK potassium channel that inhibits neuronal activity (Richmond et al 2001;Q Liu et al 2007) displayed reduced SPHK-1-GFP punctal fluorescence (Fig. 6C).…”