Résumé
Our team has been involved during the last 10 years in the molecular cloning and biophysical characterization of honneybee ion channels. We have recently identified an honeybee homologue of DSC1, the Drosophila channel 1 displaying sequence similarity to the voltagegated sodium channel (Na V ), and identified over twenty years ago. This channel was suspected to function as a non-specific cation channel with the ability to facilitate the permeation of calcium ions (Ca 2+ ). We now show that this channel exhibits strict selectivity for Ca 2+ , and defines a new family of Ca 2+ channels, called Ca V 4. We show that Ca V 4 exhibits an unprecedented type of inactivation, which depends on both an IFM motif, like Na V, and on the permeating divalent cation, like Ca V 1 channels. Ca V 4 also displays a specific pharmacology different from CaV and NaV, with an unusual response to the alkaloid veratrine. Moreover, we describe a new type of current facilitation,that increases CaV4 currents at low voltage by 2-5 fold. Our study underscores the unique profile of Ca V 4 and defines this channel as a novel class of voltage-gated Ca 2+ channel