Vassort G M, Roulet M J, Mongo K G, Ventura-Clapier R F
Eur J Cardiol. 1978 Jun;7 Suppl:17-25.
Frog heart relaxation was analysed under voltage clamp conditions as the tension decay observed after membrane potential had been stepped back to its resting value. It appeared mostly exponential with a time constant of about 190 msec. Relaxation rate decreased with the external Na concentration. It fell to 1/10 in a Na-free solution. Relaxation rate decreased also following an increase in the intracellular Na content by application of veratrine. When switching from a high to a low Na-containing solution the relaxation rate reached rapidly a value transiently higher than the steady-state's (and vice versa). In Na-free solution, adrenaline accelerated tension decay, an effect not noticeable on frog heart in Ringer solution. In frog myocardium, part of the intracellular Ca concentration decrease which occurs during each cardiac cycle directly results from a calcium extrusion carried out by the Na-Ca exchange. Such a Ca decrease, besides internal Ca storage, should play a primary role in the relaxation of contractile tissues whose cells have a large surface/volume ratio.
在电压钳制条件下，通过观察膜电位回退到静息值后张力的衰减来分析蛙心舒张情况。其衰减大多呈指数形式，时间常数约为190毫秒。舒张速率随细胞外钠离子浓度降低而下降。在无钠溶液中，舒张速率降至原来的1/10。应用藜芦碱增加细胞内钠离子含量后，舒张速率也会降低。当从高钠溶液切换到低钠溶液时，舒张速率会迅速达到一个短暂高于稳态值的值（反之亦然）。在无钠溶液中，肾上腺素会加速张力衰减，而在任氏液中的蛙心上这种作用并不明显。在蛙心肌中，每个心动周期中细胞内钙离子浓度的部分降低直接源于钠钙交换所进行的钙外流。除了细胞内钙储存外，这种钙浓度降低在具有大表面积/体积比的收缩组织舒张过程中应起主要作用。
