Small GTP-Binding Protein and Signaling on Vascular Smooth Muscle Contraction

众所周知，平滑肌收缩的信号传导受肌球蛋白轻链（MLC）磷酸化水平的调节。MLC磷酸化水平由肌球蛋白轻链激酶（MLCK）和肌球蛋白轻链磷酸酶（MLCP）的活性平衡决定。MLCK的活性依赖于Ca^<2+>/Ca 1-modulin，而MLCP的活性则通过Rho/Rho激酶调节。我们使用完整的豚鼠回肠平滑肌研究了Rho/Rho激酶在平滑肌收缩信号传导中的作用。溶血磷脂酸（LPA）是Rho的激活剂，可引起回肠纵行平滑肌和结肠带的微弱但持续的收缩，而MLC磷酸化水平无明显增加. Rho激酶抑制剂Y-27632（1 μ mol）几乎完全抑制LPA诱导的收缩. Y-27632（10 μ mol）轻微抑制ACh（1 μ mol）诱导的收缩后2分钟的激动剂。另一方面，抑制剂（10微摩尔）对高K^+（50 mM）诱导的收缩没有影响。在ACh、高K^+溶液或LPA刺激后1或10 min，细胞溶胶中rho蛋白含量下降，而洗涤剂可溶性组分中rho蛋白含量无明显变化，表明接触剂（LPA、ACh和高K^+）可诱导完整回肠平滑肌rho蛋白移位。然而，Rho激活剂的微弱收缩和Rho激酶的特异性抑制剂的抑制它们的收缩表明Rho/Rho激酶在完整豚鼠回肠平滑肌收缩中的作用不是那么重要。

It is well known that signaling on smooth muscle contraction is regulated by level of myosin light chain (MLC) phosphorylation. The level of MLC phosphorylation is determined by the balance of activities of both myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP). The activity of MLCK is dependent on Ca^<2+>/ca1modulin, whereas that of MLCP is regulated through Rho/Rho kinase. We studied a role of Rho/Rho kinase in smooth muscle contraction signaling using intact guinea-pig ileal smooth muscle.1. Lysophosphaticic acid (LPA), an activator of Rho, induced feeble, but sustained contraction in ileal longitudinal smooth muscle and taenia coli, without marked increases in MLC phosphorylation.2. Rho kinase inhibitor Y-27632 (1 micromol) inhibited LPA-induced contraction almost completely.3. Y-27632 (10 micromol) slightly inhibited ACh (1 micromol) -induced contraction at 2 min after administration of the agonist. On the other hand, the inhibitor (10 micromol) showed no effects on high K^+ (50 mM) -induced contraction.4. At 1 or 10 min after the stimulation of ACh, high K^+ solution or LPA, rho protein in thecytosol fraction decreased without significant changes in rho protein contents in detergent-soluble fraction.These results indicate that contacting agents (LPA, ACh and high K^+) induced translocation of rho protein in intact smooth muscle of ileum. However, the feeble contraction by the Rho activator and the inhibition of their contractions by the specific inhibitor of Rho kinase suggest that the role of Rho/Rho kinase on the contraction of intact guinea-pig ileal smooth muscle is not so much important.