Regulation of L-type Ca channel and phosphorylation

用蛙心室肌细胞阐明了细胞内Mg^<2+>通过A激酶磷酸化调节L型Ca通道的作用。当细胞内Mg^&lt;2+&gt;浓度低于生理水平时，<Ca.L>由于Mg^&lt;2+&gt;对L-型钙通道的阻断解除，Mg^&lt;2+&gt;可显著增强L-型钙通道电流。当细胞被A-激酶刺激磷酸化时，通道对Mg^&lt;2+&gt;阻断变得不敏感。结论：磷酸化通过对Mg^2+阻滞的充电敏感性调节心肌细胞L型Ca通道。在蛙背根神经节（DRG）神经元的L-型钙通道中没有发现这种特殊类型的Mg^&lt;2+&gt;阻滞。Mg^2+阻断的缺失与蛙DRG神经元L-型Ca通道中A-激酶的调节缺失密切相关。我还发现，修饰半胱氨酸的SH残基的膜不可渗透的甲硫基磺酸盐化合物（MTS）可以<Ca>从细胞内侧显著增加I。当<Ca>通过A-激酶刺激将I_预条件性增加至次最大水平时，未观察到这种增强作用。这表明MTS试剂影响磷酸化机制的调节步骤之一。这些结果表明，以L-型钙通道胞内区的半胱氨酸或其相关蛋白为靶点，可以为深入了解磷酸化途径的机制提供新的思路。

The role of intracellular Mg^<2+> in the regulation of L-type Ca channel through A-kinase phosphorylation was elucidated using frog ventricular myocytes. When concentration of intracellular Mg^<2+> was lowered beyond a physiological level, it enhanced L-type Ca channel current (I_<Ca.L>) remarkably due to unblock of the channel from Mg^<2+>. The channel becomes insensitive to Mg^<2+> block when cell was phosphorylated through A-kinase stimulation. It concludes that phosphorylation regulates L-type Ca channel in cardiac myocytes through charging sensitivity to Mg^<2+> block. This particular type of Mg^<2+> block was not found in L-type Ca channel in frog dorsal root ganglion (DRG) neurons. The absence of Mg^<2+> block well correlates to the absence of the regulation through A-kinase in L-type Ca channel of frog DRG neurons. I have further found that membrane impermeable methanethiosulfonate compounds (MTS) that modify SH residues of cysteine can increase I_<Ca> dramatically from the intracellular side. This enhancing effect was not seen when I_<Ca> was pre-conditionally increased to a sub-maximal level by A-kinase stimulation. This indicates that MTS reagents affect one of the regulatory steps of phosphorylation mechanism. These results indicate that we may gain a further step to understand the mechanism of phosphorylation pathway if we target cysteines of intracellular region of L-type Ca channel or its associated proteins.