title: Biophysical characterization of the honeybee DSC1 orthologue reveals a novel voltage-dependent Ca2+ channel subfamily: CaV4.
abstract: Bilaterian voltage-gated Na(+) channels (NaV) evolved from voltage-gated Ca(2+) channels (CaV). The Drosophila melanogaster Na(+) channel 1 (DSC1), which features a D-E-E-A selectivity filter sequence that is intermediate between CaV and NaV channels, is evidence of this evolution. Phylogenetic analysis has classified DSC1 as a Ca(2+)-permeable Na(+) channel belonging to the NaV2 family because of its sequence similarity with NaV channels. This is despite insect NaV2 channels (DSC1 and its orthologue in Blatella germanica, BSC1) being more permeable to Ca(2+) than Na(+) In this study, we report the cloning and molecular characterization of the honeybee (Apis mellifera) DSC1 orthologue. We reveal several sequence variations caused by alternative splicing, RNA editing, and genomic variations. Using the Xenopus oocyte heterologous expression system and the two-microelectrode voltage-clamp technique, we find that the channel exhibits slow activation and inactivation kinetics, insensitivity to tetrodotoxin, and block by Cd(2+) and Zn(2+) These characteristics are reminiscent of CaV channels. We also show a strong selectivity for Ca(2+) and Ba(2+) ions, marginal permeability to Li(+), and impermeability to Mg(2+) and Na(+) ions. Based on current ion channel nomenclature, the D-E-E-A selectivity filter, and the properties we have uncovered, we propose that DSC1 homologues should be classified as CaV4 rather than NaV2. Indeed, channels that contain the D-E-E-A selectivity sequence are likely to feature the same properties as the honeybee's channel, namely slow activation and inactivation kinetics and strong selectivity for Ca(2+) ions.
authors.affiliation: Centre de Recherche, Institut Universitaire en Santé Mentale de Québec, Quebec City, Quebec G1J 2G3, Canada.
authors.forename: Pascal
authors.initials: P
authors.lastname: Gosselin-Badaroudine
authors.affiliation: Centre de Recherche, Institut Universitaire en Santé Mentale de Québec, Quebec City, Quebec G1J 2G3, Canada.
authors.forename: Adrien
authors.initials: A
authors.lastname: Moreau
authors.affiliation: Centre de Recherche, Institut Universitaire en Santé Mentale de Québec, Quebec City, Quebec G1J 2G3, Canada.
authors.forename: Louis
authors.initials: L
authors.lastname: Simard
authors.affiliation: Institut des Biomolécules Max Mousseron, Centre National de la Recherche Scientifique UMR 5247, 1919 Montpellier, France.
authors.forename: Thierry
authors.initials: T
authors.lastname: Cens
authors.affiliation: Institut des Biomolécules Max Mousseron, Centre National de la Recherche Scientifique UMR 5247, 1919 Montpellier, France.
authors.forename: Matthieu
authors.initials: M
authors.lastname: Rousset
authors.affiliation: INRA UR 406, Abeilles et Environnement, Domaine Saint Paul - Site Agroparc, 84914 Avignon, France.
authors.forename: Claude
authors.initials: C
authors.lastname: Collet
authors.affiliation: Institut des Biomolécules Max Mousseron, Centre National de la Recherche Scientifique UMR 5247, 1919 Montpellier, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Charnet
authors.affiliation: Centre de Recherche, Institut Universitaire en Santé Mentale de Québec, Quebec City, Quebec G1J 2G3, Canada Department of Medicine, Université Laval, Quebec City, Quebec G1K 7P4, Canada mohamed.chahine@phc.ulaval.ca.
authors.forename: Mohamed
authors.identifier: 0000-0002-9500-2839
authors.initials: M
authors.lastname: Chahine
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D001516:Bees / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D018408:Patch-Clamp Techniques; D010802:Phylogeny
chemical_list: D015220:Calcium Channels