Mechanism of expression of voltage-gated sodium and calcium channels

锚蛋白g （Ankyrin-G）是一种模块化蛋白，在哺乳动物Ranvier节点和神经元初始节段的电压门控钠通道（Nav通道）聚集中起着至关重要的作用。然而，锚定蛋白g对Nav通道电生理特性的直接影响尚不清楚。在这项研究中，我们探讨了锚定蛋白g是否在改变主要位于Ranvier和初始节段节点的神经元Nav1.6通道的门控特性中起作用。单独转染人Nav1.6 cDNA的TsA201细胞表现出显著的持续钠电流（Ina-p）。另一方面，Ina-p与锚蛋白g共表达时几乎检测不到。另一种锚蛋白锚蛋白b没有表现出这样的效果。两种锚蛋白异构体嵌合体的表达表明，锚蛋白g的膜结合结构域对降低Nav1.6的Ina-p至关重要。这些结果表明，锚定蛋白g不仅通过聚集性Nav通道调节神经元的兴奋性，而且还通过直接改变其通道门控来调节神经元的兴奋性。膜电位的变化会影响离子通道和转运体，从而改变细胞内的化学条件。其他信号通路偶联膜电位已提出，但其潜在的机制尚不清楚。我们从海鞘（Ciona nestiinalis）中鉴定出一种新的蛋白，该蛋白具有与电压门控通道S1-S4片段相似的跨膜电压感应结构域和类似磷酸酶和张力同源物（PTEN）的细胞质结构域。这种蛋白质被命名为Ci-VSP（含有磷酸酶的电压传感器），显示出类似通道的“门控”电流，并直接将膜电位的变化转化为磷酸肌苷的周转。Ci-VSP中磷酸肌醇磷酸酶的活性在膜电位的生理范围内调节。免疫细胞化学研究表明，Ci-VSP在琼脂精尾膜中表达，提示其在精子功能或形态中起作用。我们的数据表明，电压传感可以在通道蛋白之外发挥作用，因此比以前所认识的更为普遍。少

Ankyrin-G, a modular protein, plays a critical role in clustering voltage-gated sodium channels (Nav channels) in nodes of Ranvier and initial segments of mammalian neurons. However, direct effects of ankyrin-G on electrophysiological properties of Nav channels remai elusive. In this study, we explored whether ankyrin-G has a role in modifying gating properties of the neuronal Nav1.6 channel that is predominantly localized at nodes of Ranvier and initial segments. TsA201 cells transfected with the human Nav1.6 cDNA alone exhibited significant persistent sodium current (Ina-p). On the other hand, Ina-p was barely detected upon co-expression with ankyrin-G. Ankyrin-B, another ankyrin, did not show such an effect. Expression of chimeras between the two isofrms of ankyrin suggests that the membrane-binding domain of ankyurin-G is critical for reducing the Ina-p of Nav1.6. These results suggest that ankyrin-G regulates neuronal excitability not only through clustering Nav channels but also … More by directly modifying their channel gating. Changes is membraine potential affect ion channels, and transporters, which then alter intracellular chemical conditions. Ohter signaling pathways coupled to membrane potential have been suggested but their underlying mechanism are unknown. We have identified a novel protein from the ascidian Ciona intestinalis which has a transmembrane voltage sensing domain homologous to the S1-S4 segments of voltage-gated channels and a cytoplasmic domain similar to phosphatase and tension homologue (PTEN). This protein, named Ci-VSP (voltage-sensor containing phosphatase), displays channel-like "gating" currents and directly translates changes in membrane potential into the turnover of phosphoinositides. The activity of the phosphoinositide phosphatase in Ci-VSP is tuned within a physiological range of membrane potential. Immunocytochemical studies show that Ci-VSP is expressed in Ciona sperm tail membranes, suggesting a role in sperm function or morphology. Our data demonstrate that voltage sensing can function beyond channel proteins and thus more ubiquitously than previously appreciated. Less