Gunst S J, Wu M F, Smith D D
Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis 46202.
Am J Physiol. 1993 Aug;265(2 Pt 1):C467-76. doi: 10.1152/ajpcell.1993.265.2.C467.
The effect of contraction history on the isotonic shortening velocity of canine tracheal smooth muscle was investigated. Muscles were contracted isometrically for 20 s at initial lengths of L(o) (length of maximal active force), 85% L(o), or 70% L(o) using electrical field stimulation. Muscles were then allowed to shorten isotonically under different afterloads either with or without first being subjected to a step decrease in length to 70% L(o). Instantaneous velocities were plotted against instantaneous muscle length during isotonic shortening. Regardless of protocol, the velocity at any muscle length during shortening was lower when the muscle was initially activated at a longer length. The isotonic shortening velocity decreased progressively during shortening at a nearly linear rate with respect to instantaneous muscle length under all conditions. Results suggest that a longer muscle length at the time of activation leads to the development of higher loads on the contractile element during subsequent shortening, resulting in a slower shortening velocity. This plasticity of the force-velocity relationship may result from cytostructural reorganization of the smooth muscle cells in response to contractile activation at different muscle lengths.
研究了收缩历史对犬气管平滑肌等张收缩速度的影响。使用电场刺激，使肌肉在初始长度为L（o）（最大主动力长度）、85%L（o）或70%L（o）时进行20秒的等长收缩。然后，让肌肉在不同后负荷下进行等张收缩，收缩前肌肉长度要么先不发生变化，要么先经历一次阶跃式下降至70%L（o）。在等张收缩过程中，将瞬时速度与瞬时肌肉长度作图。无论采用何种方案，当肌肉最初在较长长度被激活时，缩短过程中任何肌肉长度下的速度都较低。在所有条件下，等张收缩速度在缩短过程中相对于瞬时肌肉长度以近似线性的速率逐渐降低。结果表明，激活时较长的肌肉长度会导致后续缩短过程中收缩元件上产生更高的负荷，从而导致缩短速度减慢。力-速度关系的这种可塑性可能是由于平滑肌细胞在不同肌肉长度下响应收缩激活而发生的细胞结构重组所致。
