Mashima H
Jpn J Physiol. 1977;27(4):483-99. doi: 10.2170/jjphysiol.27.483.
A frog ventricular muscle strip could be fully tetanized by alternating current stimulation at 10 Hz and 20 V/cm in a solution containing 9 mM Ca2+. During isometric tetanus, the controlled release was made and the shortening velocities against various loads were measured. The isometric force was varied by reducing the stimulus intensity in K+-rich solution, or by reducing the external Ca2+ concentration. The force-load-velocity relation was described by a simple hyperbolic equation: (P+A)(v+b)=b(F+A), A=(F/Fm)a for shortening, and (2F-P+A')(-v+b')=b'(F+A'),A'=(F/Fm)a' for lengthening, where F is the isometric force, Fm is the maximum isometric force at the optimal muscle length, Lm, P is the load, v is the velocity, a, b, a' and b' are constants. The values of constants were a/Fm=0.51, b=0.75 Lm/sec for shortening and a'/Fm=0.39, b'=0.75 Lm/sec for lengthening at 20 degrees C. At muscle lengths shorter than 0.92 Lm, the internal load defined as the difference between the external load and calculated load at a given velocity increased in proportion to both the velocity and the decrease in muscle length.
在含有9 mM Ca2+的溶液中，通过10 Hz的交流电刺激和20 V/cm的电压，青蛙心室肌条可被完全强直收缩。在等长强直收缩期间，进行控制释放，并测量在不同负荷下的缩短速度。通过在富含K+的溶液中降低刺激强度或降低外部Ca2+浓度来改变等长力。力-负荷-速度关系由一个简单的双曲线方程描述：(P + A)(v + b) = b(F + A)，缩短时A = (F/Fm)a ，而(2F - P + A')(-v + b') = b'(F + A')，延长时A' = (F/Fm)a' ，其中F是等长力，Fm是在最佳肌肉长度Lm时的最大等长力，P是负荷，v是速度，a、b、a'和b'是常数。在20摄氏度时，缩短的常数取值为a/Fm = 0.51，b = 0.75 Lm/秒；延长的常数取值为a'/Fm = 0.39，b' = 0.75 Lm/秒。在肌肉长度小于0.92 Lm时，定义为外部负荷与给定速度下计算负荷之差的内部负荷与速度和肌肉长度的减少均成比例增加。
