Butler T M, Siegman M J
Fed Proc. 1983 Jan;42(1):57-61.
Experiments have been done to determine the relationships among active force output, average rate of high-energy phosphate utilization, and the degree of phosphorylation of the 20,000-dalton myosin light chain in the rabbit tenia coli at 18 C. During an isometric tetanus at l0 the degree of light chain phosphorylation increases to a maximum of 30-40% before maximum force is developed, and then phosphorylation slowly decreases while active force is maintained. During the period when there is a small decrease in degree of phosphorylation, the average rate of chemical energy usage falls by fourfold. In contrast, when the calcium concentration of the bathing medium is lowered from 1.9 to 1.0 mM a very large decrease in degree of phosphorylation is associated with only a small decrease in both energy usage and active force. At lower calcium levels both force and chemical energy usage decrease proportionately with little further decrease in degree of phosphorylation. We conclude that under isometric conditions there is no consistent relationship between degree of myosin light chain phosphorylation and the rate of cross-bridge cycling as measured by the rate of high-energy phosphate usage in this mammalian smooth muscle.
已开展实验以确定在18℃下兔结肠带中主动力输出、高能磷酸利用平均速率以及20,000道尔顿肌球蛋白轻链磷酸化程度之间的关系。在10Hz等长强直收缩期间，轻链磷酸化程度在最大力产生之前增加至最大30 - 40%，然后在维持主动力时磷酸化缓慢下降。在磷酸化程度略有下降的期间，化学能使用平均速率下降四倍。相比之下，当浴液介质中的钙浓度从1.9mM降至1.0mM时，磷酸化程度大幅下降，而能量使用和主动力仅略有下降。在较低钙水平下，力和化学能使用成比例下降，磷酸化程度几乎不再进一步下降。我们得出结论，在等长条件下，在该哺乳动物平滑肌中，肌球蛋白轻链磷酸化程度与以高能磷酸使用速率衡量的横桥循环速率之间不存在一致关系。
