Huntsman L L, Stewart D K
Circ Res. 1977 Apr;40(4):366-71. doi: 10.1161/01.res.40.4.366.
We studied changes in the relationship of isometric developed force to muscle length when extracellular calcium concentration was altered in isolated cat papillary muscles. In two series of experiments at temperatures of 30 degrees C and 32 degrees C, and rates of 12 and 30 beats/min, 21 muscles were exposed to calcium concentrations of 1.125, 2.25 and 4.5 mM. Muscle lengths were varied between 80% and 100% of the length at which maximum developed force occurred (Lmax). Peak developed force and the time from stimulus to peak were measured. The data indicate that force is not altered proportionately at all lengths when calcium concentration is changed. Rather, we found that a substantially greater modification of force occurs at short lengths than at long lengths. Similarly, the time to peak force increases with length at a rate which is more than 4 times greater at the low calcium concentration than it is at the high concentration. Small but consistent shifts of Lmax also are seen. We observed that Lmax is longer when inotropic changes reduce force and shorter when force is increased. These results indicate that the inotropic effect of extracellular calcium concentration changes is dependent on muscle length.
我们研究了在离体猫乳头肌中改变细胞外钙浓度时，等长收缩力与肌肉长度之间关系的变化。在温度为30摄氏度和32摄氏度、心率分别为12次/分钟和30次/分钟的两组实验中，21块肌肉分别暴露于钙浓度为1.125、2.25和4.5毫摩尔的环境中。肌肉长度在产生最大收缩力的长度（Lmax）的80%至100%之间变化。测量了最大收缩力峰值和从刺激到峰值的时间。数据表明，当钙浓度改变时，在所有长度下力并非按比例变化。相反，我们发现与长长度相比，在短长度时力的改变要大得多。同样，达到峰值力的时间随长度增加，在低钙浓度下的增加速率比高钙浓度下快4倍以上。还观察到Lmax有微小但一致的变化。我们发现，当变力作用降低力时Lmax更长，而当力增加时Lmax更短。这些结果表明，细胞外钙浓度变化的变力作用取决于肌肉长度。
