Driska S P, Aksoy M O, Murphy R A
Am J Physiol. 1981 May;240(5):C222-33. doi: 10.1152/ajpcell.1981.240.5.C222.
The hypothesis that Ca2+ initiates contraction in smooth muscle by activating an endogenous myosin light chain kinase (MLCK) that phosphorylates the 20,000 dalton light chain (LC 20) of myosin was tested in tissues prepared from the media of swine carotid arteries. Unstimulated tissues with low levels of tone exhibited low levels of phosphorylated LC 20. On stimulation with a high-K+ physiological salt solution containing 1.6 mM CaCl2, LC 20 phosphorylation increased to 0.6 mol P/mol LC 20 within 30 s. This increase preceded force development, which required 2-4 min to attain a maximum steady-state value of 3.34 +/- 0.15 (SE) X 10(5) N/m2. These results support the hypothesis, as the stimulus was submaximal for the preparation. However, LC 20 phosphorylation declined significantly from its peak value before steady-state force was attained, reaching near control levels after 10 min of stimulation. The results suggest that Ca2+-stimulated LC 20 phosphorylation is an important physiological control mechanism but that additional factors are involved in the maintenance of tonic isometric force.
钙离子通过激活内源性肌球蛋白轻链激酶（MLCK）使肌球蛋白的20,000道尔顿轻链（LC 20）磷酸化从而引发平滑肌收缩这一假说，在取自猪颈动脉中膜的组织中进行了验证。低张力的未受刺激组织中，磷酸化LC 20水平较低。用含1.6 mM氯化钙的高钾生理盐溶液刺激后，LC 20磷酸化在30秒内增加至0.6摩尔磷/摩尔LC 20。这种增加先于力的产生，力的产生需要2 - 4分钟达到3.34 +/- 0.15（SE）X 10(5) N/m2的最大稳态值。这些结果支持了该假说，因为该刺激对该制剂而言是次最大刺激。然而，在达到稳态力之前，LC 20磷酸化从其峰值显著下降，刺激10分钟后降至接近对照水平。结果表明，钙离子刺激引起的LC 20磷酸化是一种重要的生理控制机制，但维持紧张性等长力还涉及其他因素。
