Expression and distribution of voltage-sensitive sodium channels in pyrethroid-susceptible and pyrethroid-resistant Musca domestica

Cloning and molecular characterization of a putative voltage-gated sodium channel gene in the crayfish

Voltage-gated sodium channel genes and associated proteins have been cloned and studied in many mammalian and invertebrate species. However, there is no data available about the sodium channel gene(s) in the crayfish, although the animal has frequently been used as a model to investigate various aspects of neural cellular and circuit function. In the present work, by using RNA extracts from crayfish abdominal ganglia samples, the complete open reading frame of a putative sodium channel gene has firstly been cloned and molecular properties of the associated peptide have been analyzed. The open reading frame of the gene has a length of 5793 bp that encodes for the synthesis of a peptide, with 1930 amino acids, that is 82% similar to the α-peptide of a sodium channel in a neighboring species, Cancer borealis. The transmembrane topology analysis of the crayfish peptide indicated a pattern of four folding domains with several transmembrane segments, as observed in other known voltage-gated sodium channels. Upon analysis of the obtained sequence, functional regions of the putative sodium channel responsible for the selectivity filter, inactivation gate, voltage sensor, and phosphorylation have been predicted. The expression level of the putative sodium channel gene, as defined by a qPCR method, was measured and found to be the highest in nervous tissue.

Biochemical changes in dehydrogenase, hydroxylase and tyrosinase of a permethrin-resistant strain of housefly larvae, Musca domestica L

In the present study, a permethrin-resistant strain (ALHF) of housefly was used to understand some enzymic changes in normal biosynthetic pathways after insecticide selection. Aflatoxin B(1) (AFB(1)) as a natural substrate was used to verify the changes on the level of cytochrome P450-dependent monooxygenases and oxido-reductase activities in the ALHF strain compared to an insecticide-susceptible strain, aabys. ALHF yielded three major biotransformation products: aflatoxin B(2a) (AFB(2a)), aflatoxin M(1) (AFM(1)), and aflatoxicol (AFL) by larvae. These principal products were also found in aabys. AFL production rate of ALHF larvae was 5-fold lower than that of aabys. Differences between ALHF larvae and aabys in AFM(1) production were found. ALHF did not differ significantly from aabys in AFB(2a) production. The levels of 17α- and β-hydroxysteroid dehydrogenase (17α- and β-HSD) were also determined to elucidate which type of dehydrogenase activities could be changed. The cytosolic fraction of ALHF larvae yielded about 2-fold higher 17α-estradiol than that of aabys larvae. In contrast, the microsomal fraction of ALHF larvae produced about 2-fold lower amount of 17α-estradiol than that of aabys larvae. The production rate of microsomal fraction of 17β-estradiol ALHF larvae yielded 3-fold lower than that of aabys larvae. Inhibition studies on 17α-HSD and 17β-HSD activities by pyrethroid insecticides showed that there was no inhibition by pyrethroids on the enzyme activity. Therefore, there seems to be no changes on the enzyme structures. Changes on enzyme expression may occur in ALHF larvae in relation to 17α- or β-HSD. To assess biochemical changes of the cuticle formation phenylalanine 4-hydroxylase and tyrosinase activities were determined. The production rate of tyrosine from phenylalanine in ALHF was about 2-fold higher for larvae than that in aabys. l-(dihydroxylphenyl)alanine (DOPA) content was determined in larvae and ALHF possessed 1.6-fold larger amounts of DOPA than aabys. Tyrosinase activity of ALHF larval preparations showed 1.6-fold higher than aabys. In summary, many enzymic changes were found in ALHF strain compared to aabys strain and these changes may be resulted from the permethrin selection.