How G proteins inhibit N-type, voltage-gated, calcium-selective channels (Ca V 2.2) during presynaptic inhibition is a decades-old question. G proteins Gβγ bind to intracellular Ca V 2.2 regions, but the inhibition is voltage dependent. Using the hybrid electrophysiological and optical approach voltage-clamp fluorometry, we show that Gβγ acts by selectively inhibiting a subset of the four different Ca V 2.2 voltage-sensor domains (VSDs I to IV). During regular “willing” gating, VSD-I and -IV activations resemble pore opening, VSD III activation is hyperpolarized, and VSD II appears unresponsive to depolarization. In the presence of Gβγ, Ca V 2.2 gating is “reluctant”: pore opening and VSD I activation are strongly and proportionally inhibited, VSD IV is modestly inhibited, while VSD III is not. We propose that Gβγ inhibition of VSDs I and IV underlies reluctant Ca V 2.2 gating and subsequent presynaptic inhibition.

中文翻译：

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Ca V 2.2（N 型）通道的电压依赖性 G 蛋白调节


G 蛋白如何在突触前抑制期间抑制 N 型、电压门控、钙选择性通道 （Ca V 2.2） 是一个几十年来的问题。G 蛋白 Gβγ 与细胞内 Ca V 2.2 区结合，但抑制作用是电压依赖性的。使用混合电生理学和光学方法电压钳荧光法，我们表明 Gβγ 通过选择性抑制四个不同 Ca V 2.2 电压传感器域 （VSD I 至 IV） 的子集发挥作用。在常规的“自愿”门控期间，VSD-I 和 -IV 激活类似于孔张开，VSD III 激活是超极化的，VSD II 似乎对去极化没有反应。在 Gβγ 存在的情况下，Ca V 2.2 门控是“不情愿的”：孔隙张开和 VSD I 激活受到强烈且成比例的抑制，VSD IV 受到适度抑制，而 VSD III 则没有。我们提出 VSD I 和 IV 的 Gβγ 抑制是不情愿的 Ca V 2.2 门控和随后的突触前抑制的基础。