Butler T M, Mooers S U, Li C, Narayan S, Siegman M J
Department of Physiology, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA.
Biophys J. 1998 Oct;75(4):1904-14. doi: 10.1016/S0006-3495(98)77631-3.
Recent experiments on permeabilized anterior byssus retractor muscle (ABRM) of Mytilus edulis have shown that phosphorylation of twitchin releases catch force at pCa > 8 and decreases force at suprabasal but submaximum [Ca2+]. Twitchin phosphorylation decreases force with no detectable change in ATPase activity, and thus increases the energy cost of force maintenance at subsaturating [Ca2+]. Similarly, twitchin phosphorylation causes no change in unloaded shortening velocity (Vo) at any [Ca2+], but when compared at equal submaximum forces, there is a higher Vo when twitchin is phosphorylated. During calcium activation, the force-maintaining structure controlled by twitchin phosphorylation adjusts to a 30% Lo release to maintain force at the shorter length. The data suggest that during both catch and calcium-mediated submaximum contractions, twitchin phosphorylation removes a structure that maintains force with a very low ATPase, but which can slowly cycle during submaximum calcium activation. A quantitative cross-bridge model of catch is presented that is based on modifications of the Hai and Murphy (1988. Am. J. Physiol. 254:C99-C106) latch bridge model for regulation of mammalian smooth muscle.
最近对紫贻贝可透性前足丝牵缩肌（ABRM）进行的实验表明，肌联蛋白磷酸化在pCa > 8时释放捕捉力，并在高于基础但低于最大[Ca2+]时降低力。肌联蛋白磷酸化降低力，而ATP酶活性无明显变化，因此在亚饱和[Ca2+]时增加了维持力的能量消耗。同样，肌联蛋白磷酸化在任何[Ca2+]下都不会改变无负荷缩短速度（Vo），但在相同的亚最大力下进行比较时，肌联蛋白磷酸化时的Vo更高。在钙激活过程中，由肌联蛋白磷酸化控制的力维持结构会调整到30% Lo释放，以在较短长度下维持力。数据表明，在捕捉和钙介导的亚最大收缩过程中，肌联蛋白磷酸化都会去除一种以极低ATP酶维持力的结构，但这种结构在亚最大钙激活过程中可以缓慢循环。本文提出了一种捕捉的定量横桥模型，该模型基于对Hai和Murphy（1988年。《美国生理学杂志》254：C99 - C106）用于调节哺乳动物平滑肌的闩锁桥模型的修改。
