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(2+)-activated K(+) channel, and in
unc-43, which encodes CaM-kinase II, and a gain-of-function mutation in
egl-30, which encodes Gqalpha, 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.