Abstract
While Na V α-subunits in mammals are encoded by nine genes, two genes have been described in insects. The para gene (e.g., Drosophila melanogaster) and a second gene, called DSC1 for Drosophila Sodium Channel 1. DSC1 shares moderate sequence homology with the para gene and encodes a cation channel permeable to Ca 2+. Furthermore, no proteins with structures similar to the Na V regulatory subunits Na Vβ have been found in insects. However, TipE and four TipE homologs (TEH1-4) cloned from D. melanogaster have been shown to increase channel expression and modulate the voltage-dependence gating and inactivation kinetics of Na V, just like functional mammalian Na Vβ subunits. Many insecticides directly target the insect's ion channel activity. It is therefore essential to understand the molecular and biophysical properties of these channels. We have reported the cloning, functional expression, and biophysical and pharmacological characterization of the honeybee ( Apis mellifera) DSC1 homologue in Xenopus oocytes, which we have named AmCa V4, based on the properties uncovered and the current ion channels nomenclature (Gosselin-Badaroudine et al 2016). We report here the characterization of the honeybee ( Apis mellifera) DSC1 orthologue overexpressed in tsA201 cells using the patch-clamp technique. We show that the channel exhibits slow activation and inactivation kinetics, low-sensitivity to intracellular Ca 2+, assessed using different calcium chelating agents. Moreover, unlike other Ca V channels, Ba 2+ substitution exhibit faster kinetics than Ca 2+ currents suggesting an ion permeation modulation different from voltage-gated calcium channels. Our study supports the claims by Gosselin-Badaroudine et al. that due to the D-E-E-A selectivity filter, the insensitivity to tetrodotoxin, and block by Cd 2+ and Zn 2+, DSC1 homologues should be classified as Ca V4 rather than Na V2.