Martyn D A, Rondinone J F, Huntsman L L
Am J Physiol. 1983 May;244(5):H708-14. doi: 10.1152/ajpheart.1983.244.5.H708.
The length and time dependence of shortening velocity (VL) at a very light load (1 mN) was determined for central segments of ferret papillary muscle at 27 degrees C. A recently developed technique that measures the cross-sectional area of the chosen segment was used to assess segment length. Segment length (SL) or force could be used as a feedback control signal. VL was determined by releasing the muscle to a 1-mN load (less than or equal to 3% maximum force) at various times during a segment isometric twitch. Segment isometric twitches were typically performed at 95-98% SLmax, SLmax being the longest segment length attainable in the preparation. VL, as a function of time and SL, was determined from SL shortening during the load clamp. Muscle responses were sampled, stored, and analyzed with an on-line digital computer. The data indicate that 1) at a given SL, VL declines from 20 to 50% of its peak value by the time of peak force production, 2) VL declines linearly with SL below 90% SLmax in 1.125, 2.25, and 4.5 mM extracellular Ca2+, 3) VL exhibits a dependence on extracellular Ca2+, having peak values at 90% SLmax of 3.32 +/- 0.33, 2.66 +/- 0.17, and 1.89 +/- 0.17 SL/s in 4.5, 2.25, and 1.125 mM extracellular Ca2+, respectively.
在27摄氏度下，测定了雪貂乳头肌中央节段在非常轻的负荷（1毫牛）下缩短速度（VL）的长度和时间依赖性。使用一种最近开发的测量所选节段横截面积的技术来评估节段长度。节段长度（SL）或力可用作反馈控制信号。通过在节段等长收缩的不同时间将肌肉释放到1毫牛的负荷（小于或等于最大力的3%）来测定VL。节段等长收缩通常在95 - 98% SLmax下进行，SLmax是该制剂中可达到的最长节段长度。根据负荷钳制期间SL的缩短情况，确定VL作为时间和SL的函数。肌肉反应通过在线数字计算机进行采样、存储和分析。数据表明：1）在给定的SL下，到产生峰值力时，VL从其峰值下降20%至50%；2）在1.125、2.25和4.5 mM细胞外Ca2+中，当SL低于90% SLmax时，VL随SL呈线性下降；3）VL表现出对细胞外Ca2+的依赖性，在4.5、2.25和1.125 mM细胞外Ca2+中，90% SLmax时的峰值分别为3.32±0.33、2.66±0.17和1.89±0.17 SL/s。
