The 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.

中文翻译：

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hIKCa 通道亚基中的单个卷曲螺旋结构域突变破坏了异聚 hSK1:hIKCa 通道的优先形成

IKCa (SK4) 通道亚基的表达与 SK 通道亚基的表达重叠，并且有人提出，这两个相关的亚基更倾向于共组装形成异聚 hSK1:hIKCa 通道。这表明 hSK1:hIKCa 异聚体的生理作用可能归因于 SK 通道的激活。我们使用突变方法来确认异源 hSK1:hIKCa 通道的形成。hSK1 中残基的引入预计会赋予 hIKCa 电流阻断剂 TRAM-34 敏感性，从而改变了功能性异聚体的药理学。与野生型亚基之间形成的异聚体相比，野生型 hIKCa 和突变型 hSK1 亚基之间形成的异聚体通道对添加 TRAM-34 显示出显着更高的敏感性和最大阻断。hIKCa 通道亚基的一个 COOH 末端卷曲螺旋结构域内的单点突变破坏了异聚体形成。该突变仅破坏hSK1:hIKCa异聚通道的形成，而不影响同聚hIKCa通道的形成。最后，发现异聚hSK1:hIKCa通道的Ca ²⁺门控敏感性显着低于同聚hIKCa通道的Ca ²⁺门控敏感性。这些数据证实了亚基之间COOH末端相互作用所导致的异聚通道的优选形成。^{异聚体对 Ca 2+}激活的独特敏感性表明异聚体通道在表达两个亚基的神经元内发挥独特的功能。