Molecular characterization and functional expression of the Apis mellifera voltage-dependent Ca2+ channels

Voltage-gated Ca2+ channels allow the influx of Ca2+ ions from the extracellular space upon membrane depolarization and thus serve as a transducer between membrane potential and cellular events initiated by Ca2+ transients. Most insects are predicted to possess three genes encoding Cav alpha, the main subunit of Ca2+ channels, and several genes encoding the two auxiliary subunits, Cav beta and Cav alpha 2 delta: however very few of these genes have been cloned so far. Here, we cloned three full-length cDNAs encoding the three Cav alpha subunits (AmelCav1a, AmelCav2a and AmelCav3a), a cDNA encoding a novel variant of the Cav beta subunit (AmelCav beta c), and three full-length cDNAs encoding three Cav alpha 2 delta subunits (AmelCav alpha 2 delta 1 to 3) of the honeybee Apis mellifera. We identified several alternative or mutually exclusive exons in the sequence of the AmelCav2 and AmelCav3 genes. Moreover, we detected a stretch of glutamine residues in the C-terminus of the AmelCav1 subunit that is reminiscent of the motif found in the human Cav2.1 subunit of patients with Spinocerebellar Ataxia type 6. All these subunits contain structural domains that have been identified as functionally important in their mammalian homologues. For the first time, we could express three insect Cav alpha subunits in Xenopus oocytes and we show that AmelCav1a, 2a and 3a form Ca2+ channels with distinctive properties. Notably, the co-expression of AmelCav1a or AmelCav2a with AmelCav beta c and AmCav alpha 2 delta 1 produces High Voltage-Activated Ca2+ channels. On the other hand, expression of AmelCav3a alone leads to Low Voltage-Activated Ca2+ channels. (C) 2015 Elsevier Ltd. All rights reserved.