Maeda Yoshihisa, Hirano Katsuya, Nishimura Junji, Sasaki Tomio, Kanaide Hideo
Division of Molecular Cardiology, Research Institute of Angiocardiolgoy, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Br J Pharmacol. 2003 Nov;140(5):871-80. doi: 10.1038/sj.bjp.0705487. Epub 2003 Oct 6.
The role of Rho kinase in Ca2+ sensitization of the contractile apparatus in smooth muscle was investigated in the bovine middle cerebral artery. U46619, a thromboxane A2 analog, induced a greater sustained contraction with a smaller [Ca2+]i elevation than that seen with 118 mm K+. The level of myosin light chain (MLC) phosphorylation obtained in the initial phase of the contraction was higher than that seen with 118 mm K+; thereafter, it gradually declined to a comparable level in the late phase. During the steady state of the U46619-induced contraction, Y27632 (10 microM), a Rho-kinase inhibitor, partially inhibited [Ca2+]i, although it substantially inhibited tension and MLC phosphorylation. Wortmannin (10 microM), an MLC kinase inhibitor, had no significant effect on [Ca2+]i, but it completely inhibited MLC phosphorylation and partially inhibited tension. The wortmannin-resistant tension development was thus not associated with MLC phosphorylation, and this component was completely inhibited by Y27632. In conclusion, U46619 enhanced Ca2+ sensitivity in a manner both dependent and independent of MLC phosphorylation in the bovine middle cerebral artery. Both mechanisms of Ca2+ sensitization can be inhibited by the Rho-kinase inhibitor.
在牛大脑中动脉中研究了Rho激酶在平滑肌收缩装置钙敏化中的作用。血栓素A2类似物U46619与118 mM K⁺相比，在较小的细胞内钙浓度（[Ca²⁺]i）升高情况下诱导出更强的持续性收缩。收缩初始阶段获得的肌球蛋白轻链（MLC）磷酸化水平高于118 mM K⁺诱导的情况；此后，在后期逐渐下降至相当水平。在U46619诱导的收缩稳态期间，Rho激酶抑制剂Y27632（10 μM）部分抑制[Ca²⁺]i，尽管它显著抑制张力和MLC磷酸化。MLC激酶抑制剂渥曼青霉素（10 μM）对[Ca²⁺]i无显著影响，但它完全抑制MLC磷酸化并部分抑制张力。因此，渥曼青霉素耐药的张力发展与MLC磷酸化无关，并且该部分被Y27632完全抑制。总之，U46619以依赖和不依赖MLC磷酸化的方式增强了牛大脑中动脉的钙敏感性。两种钙敏化机制均可被Rho激酶抑制剂抑制。
