The voltage-gated calcium channel Ca_V1.1a primarily functions as voltage-sensor in skeletal muscle excitation-contraction (EC) coupling. In embryonic muscle the splice variant Ca_V1.1e, which lacks exon 29, additionally function as a genuine L-type calcium channel. Because previous work in most laboratories used a Ca_V1.1 expression plasmid containing a single amino acid substitution (R165K) of a critical gating charge in the first voltage-sensing domain (VSD), we corrected this substitution and analyzed its effects on the gating properties of the L-type calcium currents in dysgenic myotubes. Reverting K165 to R right-shifted the voltage-dependence of activation by ~12 mV in both Ca_V1.1 splice variants without changing their current amplitudes or kinetics. This demonstrates the exquisite sensitivity of the voltage-sensor function to changes in the specific amino acid side chains independent of their charge. Our results further indicate the cooperativity of VSDs I and IV in determining the voltage-sensitivity of Ca_V1.1 channel gating.

电压门控钙通道 Ca _V 1.1a 主要在骨骼肌兴奋-收缩 (EC) 耦合中充当电压传感器。在胚胎肌肉中，剪接变体 Ca _V 1.1e（缺少外显子 29）还具有真正的 L 型钙通道的功能。由于大多数实验室之前的工作使用的 Ca _V 1.1 表达质粒含有第一电压传感域 (VSD) 中关键门控电荷的单个氨基酸取代 (R165K)，因此我们纠正了这种取代并分析了其对门控特性的影响发育不良肌管中 L 型钙电流的研究。在两种 Ca _V 1.1 剪接变体中，将 K165 恢复为 R 会使激活的电压依赖性右移约 12 mV，而不会改变其电流幅度或动力学。这表明电压传感器功能对特定氨基酸侧链的变化具有极高的敏感性，而与它们的电荷无关。我们的结果进一步表明 VSD I 和 IV 在确定 Ca _V 1.1 通道门控的电压敏感性方面的协同作用。