A gain-of-function mutation in adenylate cyclase confers isoflurane resistance in Caenorhabditis elegans.
BACKGROUND
Volatile general anesthetics inhibit neurotransmitter release by a mechanism not fully understood. Genetic evidence in Caenorhabditis elegans has shown that a major mechanism of action of volatile anesthetics acting at clinical concentrations in this animal is presynaptic inhibition of neurotransmission. To define additional components of this presynaptic volatile anesthetic mechanism, C. elegans mutants isolated as phenotypic suppressors of a mutation in syntaxin, an essential component of the neurotransmitter release machinery, were screened for anesthetic sensitivity phenotypes.


METHODS
Sensitivity to isoflurane concentrations was measured in locomotion assays on adult C. elegans. Sensitivity to the acetylcholinesterase inhibitor aldicarb was used as an assay for the global level of C. elegans acetylcholine release. Comparisons of isoflurane sensitivity (measured by the EC₅₀) were made by simultaneous curve-fitting and F test.


RESULTS
Among the syntaxin suppressor mutants, js127 was the most isoflurane resistant, with an EC₅₀ more than 3-fold that of wild type. Genetic mapping, sequencing, and transformation phenocopy showed that js127 was an allele of acy-1, which encodes an adenylate cyclase expressed throughout the C. elegans nervous system and in muscle. js127 behaved as a gain-of-function mutation in acy-1 and had increased concentrations of cyclic adenosine monophosphate. Testing of single and double mutants along with selective tissue expression of the js127 mutation revealed that acy-1 acts in neurons within a Gαs-PKA-UNC-13-dependent pathway to regulate behavior and isoflurane sensitivity.


CONCLUSIONS
Activation of neuronal adenylate cyclase antagonizes isoflurane inhibition of locomotion in C. elegans.
Department of Anatomy and Neurobiology, and Division of Biology and Biomedical Sciences, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Owais
O
Saifee
Laura B
LB
Metz
Michael L
ML
Nonet
C Michael
CM
Crowder
D000109:Acetylcholine / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000235:genetics* / Q000378:metabolism; D000448:Aldicarb / Q000378:metabolism / Q000494:pharmacology; D000483:Alleles; D018685:Anesthetics, Inhalation / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D017173:Caenorhabditis elegans / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D002874:Chromosome Mapping / Q000379:methods; D004351:Drug Resistance / Q000235:genetics*; D007530:Isoflurane / Q000378:metabolism / Q000494:pharmacology*; D009154:Mutation / Q000235:genetics*; D050765:Qa-SNARE Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000235:genetics
D018685:Anesthetics, Inhalation; D050765:Qa-SNARE Proteins; D000448:Aldicarb; D007530:Isoflurane; D000262:Adenylyl Cyclases; D000109:Acetylcholine