Characterization of the first honeybee Ca²⁺ channel subunit reveals two novel species- and splicing-specific modes of regulation of channel inactivation

Pflugers Arch. 2013 Jul;465(7):985-96. doi: 10.1007/s00424-013-1223-2. Epub 2013 Apr 16.

Abstract

The honeybee is a model system to study learning and memory, and Ca(2+) signals play a key role in these processes. We have cloned, expressed, and characterized the first honeybee Ca(2+) channel subunit. We identified two splice variants of the Apis CaVβ Ca(2+) channel subunit (Am-CaVβ) and demonstrated expression in muscle and neurons. Although AmCaVβ shares with vertebrate CaVβ 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 CaV2 channels both, AmCaVβa and AmCaVβb, increase current amplitude, shift the voltage-sensitivity of the channel, and slow channel inactivation as the vertebrate CaVβ2a subunit does. However, as opposed to CaVβ2a, slow inactivation induced by Am-CaVβa 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(2+) currents in Apis neurons or muscle cells evidenced a sensitivity to PI3K inhibitors and H89, suggesting that both AmCaVβ variants may be important to couple cell signaling to Ca(2+) entry in vivo. Functional interactions with phospho-inositide and identification of phosphorylation sites in AmCaVβa and AmCaVβb N termini, respectively, suggest that AmCaVβ 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(2+) channel activity by CaVβ subunit.

MeSH terms

  • Action Potentials*
  • Alternative Splicing
  • Amino Acid Sequence
  • Animals
  • Bees / chemistry
  • Bees / genetics
  • Bees / metabolism*
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels / chemistry
  • Calcium Channels / genetics
  • Calcium Channels / metabolism*
  • Cells, Cultured
  • Exons
  • Gene Deletion
  • HEK293 Cells
  • Humans
  • Insect Proteins / chemistry
  • Insect Proteins / genetics
  • Insect Proteins / metabolism*
  • Molecular Sequence Data
  • Muscle Fibers, Skeletal / physiology
  • Neurons / physiology
  • Phosphatidylinositol 3-Kinases / pharmacology
  • Phosphoinositide-3 Kinase Inhibitors
  • Phosphorylation
  • Protein Kinase Inhibitors / pharmacology
  • Protein Structure, Tertiary
  • Protein Subunits / chemistry
  • Protein Subunits / genetics
  • Protein Subunits / metabolism
  • Xenopus

Substances

  • Calcium Channel Blockers
  • Calcium Channels
  • Insect Proteins
  • Phosphoinositide-3 Kinase Inhibitors
  • Protein Kinase Inhibitors
  • Protein Subunits