Ito S
Jpn Circ J. 1975 Jan;39(1):37-47. doi: 10.1253/jcj.39.37.
The transmembrane action potential and contractile force of isolated human atrial muscles which were obtained during cardiac surgery by using cardio-pulmonary by-pass technique here studied, compared with those of guinea pig left atrium. Force-requency curves showed a characteristic triphasic pattern, just as other mammalian atria. When extracellular calcium concentration was raised, percent change in contractile force was strengthened at high frequency of stimulation. When extracellular potassium concentration was reduced, contractile force became stronger and showed a monophasic pattern in response to increased frequency of stimulation. In a solution of lower ouabain concentration, action potential leaved unchanged or showed larger amplitude and longer durati-n. In a solution of higher or "therapeutic" concentration of ouabain, the duration of action potential was shortended, and in its "toxic" concentration, marked decreases in amplitude and duration were induced. The positive inotropic effect of ouabain was attributable to an increase in intensity of active state, because the rate of development of tension was increased without any significant change in the time to peak tension. When extracellular potassium concentration was reduced, contractile force became maximum at louer conce,tration of ouabain, and further increase of concentration induced ectopic impulse formation. In other words, atrail muscles cecame more sensitive to ouabain in a solution with decreased extracellular potassium concentration.
本研究采用体外循环技术，在心脏手术过程中获取分离的人心房肌，将其跨膜动作电位和收缩力与豚鼠左心房进行比较。力-频率曲线呈现出典型的三相模式，与其他哺乳动物的心房相同。当细胞外钙浓度升高时，在高频刺激下收缩力的百分比变化增强。当细胞外钾浓度降低时，收缩力增强，并且在刺激频率增加时呈现单相模式。在低浓度哇巴因溶液中，动作电位保持不变或幅度增大、持续时间延长。在高浓度或“治疗”浓度的哇巴因溶液中，动作电位持续时间缩短，而在“毒性”浓度下，幅度和持续时间均显著降低。哇巴因的正性肌力作用归因于活性状态强度的增加，因为张力发展速率增加，而达到峰值张力的时间无显著变化。当细胞外钾浓度降低时，在较低浓度的哇巴因作用下收缩力达到最大值，浓度进一步增加会诱发异位冲动形成。换句话说，在细胞外钾浓度降低的溶液中，心房肌对哇巴因变得更加敏感。
