Stull J T, Silver P J, Miller J R, Blumenthal D K, Botterman B R, Klug G A
Fed Proc. 1983 Jan;42(1):21-6.
Significant differences in the properties of myosin light chain phosphorylation in skeletal and smooth muscles may be important in considering the role of myosin phosphorylation in contraction. Repetitive, low-frequency stimulation of fast-twitch skeletal muscle resulted in phosphorylation of myosin light chain. Some of the factors leading to phosphorylation under these conditions include 1) partial activation of myosin light chain kinase with each stimulus, 2) a slow rate (t1/2 = 1 s) of inactivation of the kinase activity, and 3) a very slow rate of dephosphorylation by myosin light chain phosphatase. Myosin light chain phosphorylation was correlated with potentiation of isometric twitch tension in posttetanic potentiation and staircase responses. Stimulation of contraction in bovine tracheal smooth muscle by the cholinergic agonist carbachol was correlated with phosphorylation of the myosin light chain. The initial rate and maximum extent of phosphorylation during the first minute of stimulation was dependent on the concentration of carbachol. Phosphate incorporation into light chain declined after 1 min whereas isometric tension was maintained. beta-Adrenergic inhibition of tension development was accompanied by a decrease in the rate and extent of phosphorylatable myosin light chain phosphorylation but was not associated with reduced affinity of myosin light chain kinase for calcium-calmodulin.
骨骼肌和平滑肌中肌球蛋白轻链磷酸化特性的显著差异，在考虑肌球蛋白磷酸化在收缩中的作用时可能很重要。对快肌骨骼肌进行重复的低频刺激会导致肌球蛋白轻链磷酸化。在这些条件下导致磷酸化的一些因素包括：1）每次刺激时肌球蛋白轻链激酶的部分激活；2）激酶活性失活的速率较慢（t1/2 = 1秒）；3）肌球蛋白轻链磷酸酶的去磷酸化速率非常慢。在强直后增强和阶梯反应中，肌球蛋白轻链磷酸化与等长收缩张力的增强相关。胆碱能激动剂卡巴胆碱刺激牛气管平滑肌收缩与肌球蛋白轻链磷酸化相关。刺激第一分钟内磷酸化的初始速率和最大程度取决于卡巴胆碱的浓度。刺激1分钟后，轻链中的磷酸盐掺入量下降，而异长张力得以维持。β-肾上腺素能对张力发展的抑制伴随着可磷酸化肌球蛋白轻链磷酸化速率和程度的降低，但与肌球蛋白轻链激酶对钙调蛋白的亲和力降低无关。
