Functional exofacially tagged N-type calcium channels elucidate the interaction with auxiliary α2δ-1 subunits

Abstract

CaV1 and CaV2 voltage-gated calcium channels are associated with β and α2δ accessory subunits. However, examination of cell surface- associated CaV2 channels has been hampered by the lack of antibodies to cell surface-accessible epitopes and of functional exofacially tagged CaV2 channels. Here we report the development of fully functional CaV2.2 constructs containing inserted surface-accessible exofacial tags, which allow visualization of only those channels at the plasma membrane, in both a neuronal cell line and neurons. We first examined the effect of the auxiliary subunits. Although α2δ subunits copurify with CaV2 channels, it has recently been suggested that this interaction is easily disrupted and nonquantitative. We have now tested whether α2δ subunits are associated with these channels at the cell surface. We found that, whereas α2β-1 is readily observed at the plasma membrane when expressed alone, it appears absent when coexpressed with CaV2.2/ β1b, despite our finding that α2δ-1 increases plasmamembrane CaV2.2 expression. However, this was due to occlusion of the antigenic epitope by association with CaV2.2, as revealed by antigen retrieval; thus, our data provide evidence for a tight interaction between α2δ-1 and the α1 subunit at the plasma membrane. We further show that, although CaV2.2 cell-surface expression is reduced by gabapentin in the presence of wild-type α2δ-1 (but not a gabapentin-insensitive α2δ-1 mutant), the interaction between CaV2.2 and α2β-1 is not disrupted by gabapentin. Altogether, these results demonstrate that CaV2.2 and α2δ- 1 are intimately associated at the plasmamembrane and allowus to infer a region of interaction.