The voltage sensor of excitation-contraction coupling in mammals: Inactivation and interaction with Ca2+
The voltage sensor of excitation-contraction coupling in mammals: Inactivation and interaction with Ca2+
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DOI：
10.1085/jgp.201611725
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发表时间：
2017-11-01
影响因子：
3.8
通讯作者：
Brum, Gustavo
中科院分区：
文献类型：
--
作者：
Ferreira Gregorio, Juan;Pequera, German;Brum, Gustavo
在骨骼肌中，CaV1.1钙通道的四螺旋电压敏感模块（VSM）同时门控两个Ca 2+途径：CaV1.1孔本身和肌浆网中的RyR 1钙释放通道。在这里，为了深入了解VSMs门RyR 1的机制，我们量化了与小鼠和大鼠单个肌肉细胞中VSM激活（感测电流）和门控Ca 2+释放通量相关的膜内电荷运动。如对大多数四螺旋VSM所发现的，在持续去极化后，啮齿动物VSM失去激活Ca 2+释放通道开放的能力;它们的性质从功能上有能力的模式（其中移动的传感器电荷被称为电荷1）改变为失活模式（电荷2），其中电压依赖性向更负的电压偏移。我们发现，电荷2被促进和钙释放失活时，休息，良好极化的肌肉细胞暴露于低细胞外[Ca 2 +]，而相反的情况发生在高[Ca 2 +]。由此可见，小鼠VSM在休息时部分失活，这确立了电压感知的可用性降低作为钙血症疾病的致病机制。我们还发现，静息失活的程度是显着不同的两种小鼠品系，这强调了电压传感器的特性和它们的脆弱性，以环境条件的变化。我们的研究表明，静息和激活状态的VSMs同样有利于细胞外Ca 2+。促进由细胞外物种的两种状态的VSM，不同的构象的激活门需要存在第二个门，失活，拓扑胞外，因此可从外部访问，无论激活状态。
In skeletal muscle, the four-helix voltage-sensing modules (VSMs) of CaV1.1 calcium channels simultaneously gate two Ca2+ pathways: the CaV1.1 pore itself and the RyR1 calcium release channel in the sarcoplasmic reticulum. Here, to gain insight into the mechanism by which VSMs gate RyR1, we quantify intramembrane charge movement associated with VSM activation (sensing current) and gated Ca2+ release flux in single muscle cells of mice and rats. As found for most four-helix VSMs, upon sustained depolarization, rodent VSMs lose the ability to activate Ca2+ release channels opening; their properties change from a functionally capable mode, in which the mobile sensor charge is called charge 1, to an inactivated mode, charge 2, with a voltage dependence shifted toward more negative voltages. We find that charge 2 is promoted and Ca2+ release inactivated when resting, well-polarized muscle cells are exposed to low extracellular [Ca2+] and that the opposite occurs in high [Ca2+]. It follows that murine VSMs are partly inactivated at rest, which establishes the reduced availability of voltage sensing as a pathogenic mechanism in disorders of calcemia. We additionally find that the degree of resting inactivation is significantly different in two mouse strains, which underscores the variability of voltage sensor properties and their vulnerability to environmental conditions. Our studies reveal that the resting and activated states of VSMs are equally favored by extracellular Ca2+. Promotion by an extracellular species of two states of the VSM that differ in the conformation of the activation gate requires the existence of a second gate, inactivation, topologically extracellular and therefore accessible from outside regardless of the activation state.