Role of Myosin Light-Chain Kinase in the Regulation of Endothelial Functions and Calcium Signaling

平滑肌肌球蛋白轻链激酶（MLCK）的激活引起收缩。在这里，我们已经证明MLCK控制内皮细胞（ECs）的Ca^<2+>进入（CE）： MLCK反义寡核苷酸强烈阻止缓激肽（BK）和thapsigargin （TG）诱导的内皮细胞Ca^<2+>反应，而MLCK则没有。我们还发现相关机制不是肌球蛋白轻链（MLC）的磷酸化：BK对MLC的磷酸化需要CE，但磷酸酶抑制剂calyculin A引起的MLC磷酸化不会触发Ca^<2+>反应。最重要的是，我们首次提供了强有力的证据表明，与其在平滑肌细胞中的作用相反，在ECs中激活MLCK可以刺激重要的内皮来源的血管松弛因子的产生：MLCK反义和MLCK抑制剂可以消除BK和tg诱导的一氧化氮的产生，MLCK抑制剂可以显著抑制大鼠肠系膜动脉中乙酰胆碱刺激的平滑肌细胞膜的超极化。这些结果表明，MLCK控制内皮CE，但不是通过MLC磷酸化，并揭示了该酶迄今未知的生理功能：通过其在内皮细胞中的作用进行血管舒张。该研究发现了MLCK在血管张力调节中的平衡作用。

Activation of smooth muscle myosin light-chain kinase (MLCK) causes contraction. Here we have proven that MLCK controls Ca^<2+> entry (CE) in endothelial cells (ECs) : MLCK antisense oligonucleotides strongly prevented bradykinin (BK)- and thapsigargin (TG)-induced endothelial Ca^<2+> response while MLCK sense did not. We also show that the relevant mechanism is not phosphorylation of myosin light-chain (MLC) : MLC phosphorylation by BK required CE, but MLC phosphorylation caused by the phosphatase inhibitor calyculin A did not trigger Ca^<2+> response. Most importantly, we provide for the first time strong evidence that, in contrast to its role in smooth muscle cells, activation of MLCK in ECs stimulates the production of important endothelium-derived vascular relaxing factors : MLCK antisense and MLCK inhibitors abolished BK- and TG-induced nitric oxide production, and MLCK inhibitors substantially inhibited acetylcholine-stimulated hyperpolarization of smooth muscle cell membrane in rat mesenteric artery. These results indicate that MLCK controls endothelial CE, but not through MLC phosphorylation, and unveil a hitherto unknown physiological function of the enzyme : vasodilation through its action in endothelial cells. The study discovers a counter-balancing role of MLCK in the regulation of vascular tone.