Mashima H
Jpn J Physiol. 1977;27(3):321-35. doi: 10.2170/jjphysiol.27.321.
Complete tetanic contraction was generated in frog ventricular muscle by repetitive electrical stimulation. The maximum stimulus was a transverse alternating current at 10 Hz and 17-20 V/cm in peak to peak voltage in an external solution containing 9 mM Ca2+. The maximum isometric tension thus obtained was twice or more than that of the twitch tension at 20 degrees C. The tetanic tension and its rate of rise declined with decreasing external Ca2+ concentration and less than half of the maximum tension was generated at 1.8 mM Ca2+. Various tetanic tensions less than the maximum were obtained in the partially depolarized muscle in excess K+ solution by reducing the stimulus intensity. Adrenaline (5X10(-6)g/ml) potentiated the submaximal tetanic tension as well as the twitch tension, although no effect was observed for the maximum tetanic tension. The tension-length relation for the tetanic contraction of ventricular muscle was similar to that of the skeletal muscle, but the tension fell almost linearly at shorter lengths than 0.9 Lm, where Lm is the optimum length at which the maximum tension, Fm, was generated. Fm was 4.6 g/mm2, while the sarcomere length at Lm was 2.0-2.2 mum.
通过重复电刺激在蛙心室肌中产生完全强直收缩。最大刺激是在含有9 mM Ca2+的外部溶液中，频率为10 Hz、峰峰值电压为17 - 20 V/cm的横向交流电。在20℃时，由此获得的最大等长张力是单收缩张力的两倍或更多。随着外部Ca2+浓度降低，强直张力及其上升速率下降，在1.8 mM Ca2+时产生的张力不到最大张力的一半。通过降低刺激强度，在过量K+溶液中部分去极化的肌肉中可获得各种小于最大张力的强直张力。肾上腺素（5×10(-6)g/ml）增强了次最大强直张力以及单收缩张力，尽管对最大强直张力没有观察到影响。心室肌强直收缩的张力-长度关系与骨骼肌相似，但在长度小于0.9 Lm时张力几乎呈线性下降，其中Lm是产生最大张力Fm的最佳长度。Fm为4.6 g/mm2，而Lm处的肌节长度为2.0 - 2.2μm。
