Sensitivity to diethylether anesthesia of fruit flies primarily depends on the genotypes of the sodium channel gene rather than the states of the membranes and the mechanisms might be different from heat-induced paralysis

Abstract

The para locus of Drosophila melanogaster encodes the α subunit of a voltage-sensitive sodium channel. Many of the mutants develop paralysis at the high temperature (37°C) and are hypersensitive to diethylether anesthesia. We examined whether the two aspects of the phenotype are mediated by a same mechanism that involves the sodium channel molecule by investigating properties of the three para alleles ( para hd838 , para ts1 and para ts3 ). Larvae of the all para strains showed almost normal sensitivities to diethylether anesthesia while adult flies of them showed hypersensitivities to that in the following manner: para hd838 ≦ para ts1 < para ts3 < Canton-S. Larvae of the two para strains showed hypersensitivities to heat-induced paralysis in the following manner: para ts1 = para ts3 < para hd838 = Canton-S, while adult flies of the all para strains showed hypersensitivities to that in the following manner: para ts1 = para ts3 < para hd838 < Canton-S. The distinct phenotype of para hd838 from para ts1 or para ts3 observed in the larval and adult heat-induced paralysis, would be the reflection of the difference of the mutation sites between in para hd838 and para ts1 or para ts3 . In addition, because the rank of sensitivity in the adult anesthesia and heat-induced paralysis were reversed between para hd838 and para ts1 or para ts3 , the mechanisms of diethylether anesthesia and heat-induced paralysis are not the same. There would be the anesthesia-specific mechanisms because the sensitivity to anesthesia became more remarkable in para hd838 than in para ts1 or para ts3 . para hd838 has an insertion of P-element, one of a transposable element, in the second intron of the para sodium channel gene. Excision of the P-element from the para locus of the para hd838 conferred the flies the wild-typic phenotype and reduction of the para gene in para hd838 dramatically enhanced the hypersensitivity to anesthesia, suggesting that the phenotype of the strain was caused exclusively by the mutation of the para locus. The susceptibility to anesthesia also depends on the temperature at which the flies were assayed, not at which they were cultured, but the dependence on the assay temperature was smaller than that on the genotype. By these findings we could assure that the sensitivity to diethylether anesthesia of para hd838 primarily depends on the genotypes of the sodium channel gene rather than other reasons such as the fluidity of the membranes.