Kawata H, Ohba M, Hatae J, Kishi M
J Mol Cell Cardiol. 1983 May;15(5):281-93. doi: 10.1016/0022-2828(83)91340-8.
Hypertonic solutions were found to exhibit both positive and negative inotropic effects on the contraction of the isolated atrial myocardium of bullfrog. The optimum tonicity for twitch potentiation was about 1.5 T. The mechanism for the positive inotropic action was investigated. The possibility of involvement of an increase in calcium influx during each action potential was excluded, since both the overshoot and the plateau of action potential were strongly depressed by perfusion of hypertonic solution. The effect on the time course of twitch potentiation was similar to that of muscle shrinkage, regardless of the type solute (sucrose, NaCl or LiCl) used for elevating the tonicity, except that excess sodium showed an initial rapid inhibitory phase of contraction. A marked post-rest potentiation was observed even after "zero" calcium perfusion, provided that the tonicity of the bathing medium was elevated previously. Potassium contracture occurred during the prolonged hypertonic perfusion in "zero" calcium condition. In addition, caffeine contracture was strongly augmented in hypertonic solution. The results suggest that an elevation in both the [Ca2+]i and amount of calcium bound intracellularly may play an important role in the positive inotropic action.
研究发现，高渗溶液对牛蛙离体心房肌的收缩表现出正性和负性变力作用。增强抽搐的最佳张力约为1.5T。对正性变力作用的机制进行了研究。由于高渗溶液灌注会强烈抑制动作电位的超射和平台期，因此排除了每次动作电位期间钙内流增加的可能性。无论用于提高张力的溶质类型（蔗糖、氯化钠或氯化锂）如何，对抽搐增强时间进程的影响与肌肉收缩的影响相似，只是过量的钠表现出最初快速的收缩抑制期。即使在“零”钙灌注后，只要先前提高了浴液的张力，也会观察到明显的静息后增强。在“零”钙条件下长时间高渗灌注期间会发生钾挛缩。此外，咖啡因挛缩在高渗溶液中会强烈增强。结果表明，细胞内钙离子浓度（[Ca2+]i）和细胞内结合钙量的增加可能在正性变力作用中起重要作用。
