Resistance to Volatile Anesthetics by Mutations Enhancing Excitatory Neurotransmitter Release in Caenorhabditis elegans

Abstract

The molecular mechanisms whereby volatile general anesthetics (VAs) disrupt behavior remain undefined. In Caenorhabditis elegans mutations in the gene unc-64, which encodes the presynaptic protein syntaxin 1A, produce large allele-specific differences in VA sensitivity. UNC-64 syntaxin normally functions to mediate fusion of neurotransmitter vesicles with the presynaptic membrane. The precise role of syntaxin in the VA mechanism is as yet unclear, but a variety of results suggests that a protein interacting with syntaxin to regulate neurotransmitter release is essential for VA action in C. elegans. To identify additional proteins that function with syntaxin to control neurotransmitter release and VA action, we screened for suppressors of the phenotypes produced by unc-64 reduction of function. Loss-of-function mutations in slo-1, which encodes a Ca 2ϩ -activated K ϩ channel, and in unc-43, which encodes CaM-kinase II, and a gainof-function mutation in egl-30, which encodes Gq␣, were isolated as syntaxin suppressors. The slo-1 and egl-30 mutations conferred resistance to VAs, but unc-43 mutations did not. The effects of slo-1 and egl-30 on VA sensitivity can be explained by their actions upstream or parallel to syntaxin to increase the level of excitatory neurotransmitter release. These results strengthen the link between transmitter release and VA action.

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 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).…”

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

“…A, Representative traces of mPSCs and ePSCs from wild type (WT), with neuron-and muscle-specific rescue (NϩM), unc-43(lf) with neuron-specific rescue (N), and unc-43(lf) with muscle-specific rescue (M). 2001); (2) lf mutants of both slo-1 and unc-43 have been isolated in the same genetic screen as suppressors of the lethargic phenotype of a hypomorphic syntaxin mutant (Wang et al, 2001;Hawasli et al, 2004); and (3) lf mutants of both slo-1 and unc-43 are hypersensitive to the cholinesterase inhibitor aldicarb (Wang et al, 2001;Hawasli et al, 2004). Because SLO-1 dysfunction completely reversed the inhibitory effect of unc-43(gf) on neurotransmitter release, SLO-1 is likely the primary molecular target through which presynaptic UNC-43 downregulates the release.…”

“…We also analyzed mPSCs and ePSCs at the NMJ of unc-43(js125), a putative null with the first 10 exons deleted (Hawasli et al, 2004). If the function of presynaptic UNC-43 at the NMJ is only to downregulate neurotransmitter release, we would expect to see -43(gf) and each of the three double mutants (filled columns).…”

The concentration-dependent effects of ethanol on Caenorhabditis elegans behaviour

“…In this context, it is interesting to note that slo-1 mutations confer resistance to volatile anaesthetics. 24 Further studies are required on the susceptibility of slo-1 mutants to low concentrations of ethanol to resolve whether this is a genetic determinant of intoxication and/ or anaesthesia.…”