Zou H, Ratz P H, Hill M A
Department of Physiology, Eastern Virginia Medical School, Norfolk, Va., USA.
J Vasc Res. 2000 Nov-Dec;37(6):556-67. doi: 10.1159/000054089.
Previous studies demonstrated that maintenance of steady-state myogenic tone requires Ca(2+)-dependent myosin phosphorylation. The present studies furthered these observations by examining temporal relationships among Ca(2+), myosin phosphorylation and vessel diameter during acute increases in intraluminal pressure and norepinephrine stimulation. Rat cremaster muscle arterioles were cannulated and loaded with the Ca(2+)-sensitive indicator fura-2. The extent of myosin phosphorylation was measured using two-dimensional gel electrophoresis. Acute increases in intraluminal pressure caused a biphasic increase in intracellular Ca(2+) (Ca(2+)), characterized by a transient peak followed by a decline to a steady-state level which remained significantly higher than control values. Peak Ca(2+) was significantly related to vessel distension and increased with the change in wall tension. Increased intraluminal pressure resulted in a monophasic increase in myosin phosphorylation that was significantly correlated with instantaneous wall tension. In general, norepinephrine induced larger Ca(2+) transients and a biphasic myosin phosphorylation pattern. The results demonstrate: (a) major roles for Ca(2+) and myosin phosphorylation in arteriolar myogenic and norepinephrine-induced responses; (b) that changes in Ca(2+) and phosphorylation during a myogenic response are related to changes in wall tension, and (c) differences in Ca(2+) and phosphorylation patterns between the two modes of contraction reflect possible differences in underlying signaling mechanisms. The data further emphasize that spontaneous arteriolar tone represents a state of maintained smooth muscle activation that requires increases in Ca(2+) and myosin light-chain phosphorylation.
先前的研究表明，维持稳态肌源性张力需要钙离子依赖的肌球蛋白磷酸化。本研究通过检测管腔内压力急性升高和去甲肾上腺素刺激期间钙离子、肌球蛋白磷酸化和血管直径之间的时间关系，进一步拓展了这些观察结果。将大鼠提睾肌小动脉插管，并加载钙离子敏感指示剂fura-2。使用二维凝胶电泳测量肌球蛋白磷酸化程度。管腔内压力急性升高导致细胞内钙离子浓度（Ca(2+)）呈双相增加，其特征是出现一个短暂峰值，随后下降至稳态水平，该稳态水平仍显著高于对照值。峰值Ca(2+)与血管扩张显著相关，并随壁张力的变化而增加。管腔内压力升高导致肌球蛋白磷酸化呈单相增加，这与瞬时壁张力显著相关。一般来说，去甲肾上腺素诱导更大的Ca(2+)瞬变和双相肌球蛋白磷酸化模式。结果表明：（a）钙离子和肌球蛋白磷酸化在小动脉肌源性和去甲肾上腺素诱导反应中起主要作用；（b）肌源性反应期间钙离子和磷酸化的变化与壁张力的变化有关；（c）两种收缩模式之间钙离子和磷酸化模式的差异反映了潜在信号机制可能存在的差异。这些数据进一步强调，自发性小动脉张力代表一种维持平滑肌激活的状态，这需要Ca(2+)和肌球蛋白轻链磷酸化增加。
