Manville Rían W, Neverisky Daniel L, Abbott Geoffrey W
Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, Irvine, California.
Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, Irvine, California.
Biophys J. 2017 Aug 8;113(3):613-626. doi: 10.1016/j.bpj.2017.06.055.
Voltage-gated potassium channels of the KCNQ (Kv7) subfamily are essential for control of cellular excitability and repolarization in a wide range of cell types. Recently, we and others found that some KCNQ channels functionally and physically interact with sodium-dependent solute transporters, including myo-inositol transporters SMIT1 and SMIT2, potentially facilitating various modes of channel-transporter signal integration. In contrast to indirect effects such as channel regulation by SMIT-transported, myo-inositol-derived phosphatidylinositol 4,5-bisphosphate (PIP), the mechanisms and functional consequences of the physical interaction of channels with transporters have been little studied. Here, using co-immunoprecipitation with different channel domains, we found that SMIT1 binds to the KCNQ2 pore module. We next tested the effects of SMIT1 co-expression, in the absence of extracellular myo-inositol or other SMIT1 substrates, on fundamental functional attributes of KCNQ2, KCNQ2/3, KCNQ1, and KCNQ1-KCNE1 channels. Without exception, SMIT1 altered KCNQ ion selectivity, sensitivity to extracellular K, and pharmacology, consistent with an impact on conformation of the KCNQ pore. SMIT1 also altered the gating kinetics and/or voltage dependence of KCNQ2, KCNQ2/3, and KCNQ1-KCNE1. In contrast, SMIT1 had no effect on Kv1.1 (KCNA1) gating, ion selectivity, or pharmacology. We conclude that, independent of its transport activity and indirect regulatory mechanisms involving inositol-derived increases in PIP, SMIT1, and likely other related sodium-dependent solute transporters, regulates KCNQ channel ion selectivity, gating, and pharmacology by direct physical interaction with the pore module.
KCNQ（Kv7）亚家族的电压门控钾通道对于控制多种细胞类型的细胞兴奋性和复极化至关重要。最近，我们和其他人发现，一些KCNQ通道在功能和物理上与钠依赖性溶质转运体相互作用，包括肌醇转运体SMIT1和SMIT2，这可能促进通道-转运体信号整合的各种模式。与诸如由SMIT转运的肌醇衍生的磷脂酰肌醇4,5-二磷酸（PIP）对通道的间接调节作用相反，通道与转运体物理相互作用的机制和功能后果鲜有研究。在这里，我们使用与不同通道结构域的共免疫沉淀方法，发现SMIT1与KCNQ2孔模块结合。接下来，我们测试了在没有细胞外肌醇或其他SMIT1底物的情况下，SMIT1共表达对KCNQ2、KCNQ2/3、KCNQ1和KCNQ1-KCNE1通道基本功能特性的影响。无一例外，SMIT1改变了KCNQ的离子选择性、对细胞外钾的敏感性和药理学特性，这与对KCNQ孔构象的影响一致。SMIT1还改变了KCNQ2、KCNQ2/3和KCNQ1-KCNE1的门控动力学和/或电压依赖性。相比之下，SMIT1对Kv1.1（KCNA1）的门控、离子选择性或药理学没有影响。我们得出结论，独立于其转运活性和涉及肌醇衍生的PIP增加的间接调节机制，SMIT1以及可能其他相关的钠依赖性溶质转运体，通过与孔模块的直接物理相互作用来调节KCNQ通道的离子选择性、门控和药理学特性。
