Arner A, Hellstrand P
J Physiol. 1985 Mar;360:347-65. doi: 10.1113/jphysiol.1985.sp015621.
Mechanical properties and rate of ATP breakdown (JATP) have been determined in the chemically skinned guinea-pig taenia coli at 22 degrees C. The influence of varied [Ca2+], [Mg ATP] and muscle length were investigated. The shortening response after a step decrease in force (isotonic quick release) was highly curvilinear in the first 100-200 ms. This effect was shown to be a time-dependent response to the force step and not primarily caused by the shift along the length-force relation associated with shortening. Maximal shortening velocity (Vmax) decreased gradually following the release. At pCa (= -log [Ca2+]) 4.5, Vmax at 20 and 1000 ms after release was 0.49 +/- 0.07 and 0.041 +/- 0.004 (mean +/- S.E. of mean, n = 5) lengths s-1 respectively. Unloaded shortening velocity obtained from length steps of different magnitude (slack test) also showed a gradual decrease after the release, consistent with the isotonic release results. Increasing [Ca2+] from the relaxed state at pCa 9 (1 microM-calmodulin present) gave increased isometric force to a maximum at pCa 4.5. Half-maximal response was obtained at pCa 6.1. JATP at maximal force at pCa 4.5 was about 3 times the basal rate at pCa 9. The relation between JATP and force was highly non-linear, with a marked increase in JATP with little alteration in force at the highest [Ca2+]. When force was reduced to zero at pCa 4.5 by shortening the muscle to 0.3 L0 (L0 being the length giving maximal active force), JATP decreased by about 30%. At two levels of [Ca2+] giving similar force (pCa 5.75 and 4.5) the energetic tension cost obtained by length variations was lower at the low [Ca2+]. At pCa 6.0, Vmax and force were decreased to the same extent relative to their values at pCa 4.5. At pCa 5.75, where there was no reduction in force but a 25% decrease in isometric JATP, Vmax was unchanged relative to pCa 4.5. Force, Vmax and JATP were all dependent on [Mg ATP]. Half-maximal response was obtained at 0.1 mM for force and Vmax, and at 0.5 mM for JATP. The results are discussed in relation to a possible influence of both Ca2+ and Mg ATP on kinetic properties of the cross-bridge cycle.
在22摄氏度下，对化学去膜的豚鼠结肠带进行了力学性能和ATP分解速率（JATP）的测定。研究了不同的[Ca2+]、[Mg ATP]和肌肉长度的影响。在力阶跃下降（等张快速释放）后的最初100 - 200毫秒内，缩短响应呈高度曲线关系。这种效应被证明是对力阶跃的时间依赖性响应，而不是主要由与缩短相关的长度 - 力关系的变化引起的。释放后最大缩短速度（Vmax）逐渐降低。在pCa（= -log[Ca2+]）4.5时，释放后20毫秒和1000毫秒时的Vmax分别为0.49±0.07和0.041±0.004（平均值±平均标准误，n = 5）长度·秒-1。从不同幅度的长度阶跃（松弛试验）获得的无负荷缩短速度在释放后也显示出逐渐降低，这与等张释放结果一致。从pCa 9（存在1 microM钙调蛋白）的松弛状态增加[Ca2+]，等长力增加，在pCa 4.5时达到最大值。在pCa 6.1时获得半最大响应。在pCa 4.5时最大力下的JATP约为pCa 9时基础速率的3倍。JATP与力之间的关系高度非线性，在最高[Ca2+]时JATP显著增加而力变化不大。当在pCa 4.5时通过将肌肉缩短至0.3L0（L0为产生最大主动力的长度）将力降至零时，JATP降低约30%。在两个产生相似力的[Ca2+]水平（pCa 5.75和4.5）下，通过长度变化获得的能量张力成本在低[Ca2+]时较低。在pCa 6.0时，Vmax和力相对于它们在pCa 4.5时的值下降到相同程度。在pCa 5.75时，力没有降低，但等长JATP降低了25%，Vmax相对于pCa 4.5保持不变。力、Vmax和JATP都依赖于[Mg ATP]。力和Vmax在0.1 mM时获得半最大响应，JATP在0.5 mM时获得半最大响应。结合Ca2+和Mg ATP对横桥循环动力学特性的可能影响对结果进行了讨论。
