A single coiled‐coil domain mutation in hIKCa channel subunits disrupts preferential formation of heteromeric hSK1:hIKCa channels

Abstract

AbstractThe expression of IKCa (SK4) channel subunits overlaps with that of SK channel subunits, and it has been proposed that the two related subunits prefer to co‐assemble to form heteromeric hSK1:hIKCa channels. This implicates hSK1:hIKCa heteromers in physiological roles that might have been attributed to activation of SK channels. We have used a mutation approach to confirm formation of heterometric hSK1:hIKCa channels. Introduction of residues within hSK1 that were predicted to impart sensitivity to the hIKCa current blocker TRAM‐34 changed the pharmacology of functional heteromers. Heteromeric channels formed between wildtype hIKCa and mutant hSK1 subunits displayed a significantly higher sensitivity and maximum block to addition of TRAM‐34 than heteromers formed between wildtype subunits. Heteromer formation was disrupted by a single point mutation within one COOH‐terminal coiled‐coil domain of the hIKCa channel subunit. This mutation only disrupted the formation of hSK1:hIKCa heteromeric channels, without affecting the formation of homomeric hIKCa channels. Finally, the Ca2+ gating sensitivity of heteromeric hSK1:hIKCa channels was found to be significantly lower than the Ca2+ gating sensitivity of homomeric hIKCa channels. These data confirmed the preferred formation of heteromeric channels that results from COOH‐terminal interactions between subunits. The distinct sensitivity of the heteromer to activation by Ca2+ suggests that heteromeric channels fulfil a distinct function within those neurons that express both subunits.