Characterization of the first honeybee Ca^sup 2+^ channel subunit reveals two novel species- and splicing-specific modes of regulation of channel inactivation

• Published in: Pflügers Archiv 2013-07, Vol.465 (7), p.985
• Main Authors: Cens, Thierry, Rousset, Matthieu, Collet, Claude, Raymond, Valérie, Démares, Fabien, Quintavalle, Annabelle, Bellis, Michel, Le Conte, Yves, Chahine, Mohamed, Charnet, Pierre
• Format: Article
• Language: English
• ISSN: 0031-6768; 1432-2013
• DOI: 10.1007/s00424-013-1223-2

The honeybee is a model system to study learning and memory, and Ca^sup 2+^ signals play a key role in these processes. We have cloned, expressed, and characterized the first honeybee Ca^sup 2+^ channel subunit. We identified two splice variants of the Apis Ca^sub V^[beta] Ca^sup 2+^ channel subunit (Am-Ca^sub V^[beta]) and demonstrated expression in muscle and neurons. Although AmCa^sub V^[beta] shares with vertebrate Ca^sub V^[beta] subunits the SH3 and GK domains, it beholds a unique N terminus that is alternatively spliced in the first exon to produce a long (a) and short (b) variant. When expressed with the Ca^sub V^2 channels both, AmCa^sub V^[beta]a and AmCa^sub V^[beta]b, increase current amplitude, shift the voltage-sensitivity of the channel, and slow channel inactivation as the vertebrate Ca^sub V^[beta]^sub 2a^ subunit does. However, as opposed to Ca^sub V^[beta]^sub 2a^, slow inactivation induced by Am-Ca^sub V^[beta]a was insensitive to palmitoylation but displayed a unique PI3K sensitivity. Inactivation produced by the b variant was PI3K-insensitive but staurosporine/H89-sensitive. Deletion of the first exon suppressed the sensitivity to PI3K inhibitors, staurosporine, or H89. Recording of Ba^sup 2+^ currents in Apis neurons or muscle cells evidenced a sensitivity to PI3K inhibitors and H89, suggesting that both AmCa^sub V^[beta] variants may be important to couple cell signaling to Ca^sup 2+^ entry in vivo. Functional interactions with phospho-inositide and identification of phosphorylation sites in AmCa^sub V^[beta]a and AmCa^sub V^[beta]b N termini, respectively, suggest that AmCa^sub V^[beta] splicing promoted two novel and alternative modes of regulation of channel activity with specific signaling pathways. This is the first description of a splicing-dependent kinase switch in the regulation of Ca^sup 2+^ channel activity by Ca^sub V^[beta] subunit.[PUBLICATION ABSTRACT]