Löhn M, Szymanski G, Markwardt F
Julius-Bernstein-Institut für Physiologie, Martin-Luther-Universität Halle-Wittenberg, Germany.
Mol Cell Biochem. 1996 Jul-Aug;160-161:13-25. doi: 10.1007/BF00240026.
Concentrations of 1-4 mumol l-1 isoproterenol cause both in right ventricular papillary muscles and in enzymatically isolated myocytes of the guinea-pig a Ca2+ overload-induced state which is functionally characterized by biphasic (multiphasic) twitches and biphasic (multiphasic) intracellular calcium transients, respectively, during excitation-contraction coupling. This state was stabilized in the in vitro experiments for some hours by a co-ordination of the interstimulus interval, the temperature of the superfusion fluid and the addition of calcium agonists. The functional stability is the precondition for the reproducibility of the experimental results particularly after the application of long-lasting stimulation programmes. Changes in the shape of biphasic contractions were compared with changes in the time course of biphasic intracellular calcium transients using three manipulations of a different kind: (1) the interruption of the steady pacing rhythm, (2) the variation of the interstimulus interval, (3) the addition of ryanodine. It was shown that: (1) The BOWDITCH staircase in calcium overloaded multicellular preparations is changed in that each individual component of the twitch passes through its own staircase. A homologous behaviour can be observed in the configuration of the phasic and tonic component of biphasic intracellular calcium transients. (2) At different driving frequencies the relative proportion of the two components of a biphasic twitch corresponds to the time integrals of the two components of biphasic intracellular calcium transients. (3) Ryanodine suppresses both the first component of the biphasic twitch and the phasic component of the biphasic intracellular calcium transient. The SR Ca(2+)-ATPase inhibitor thapsigargin increases the second component of the biphasic calcium transient. This supports the hypothesis that the size of the tonic component is in part determined by intracellular calcium reuptake. The results of both kinds of experiments would be compatible with the assumption that in calcium overloaded mammalian cardiac cells calcium reaches the contractile system directly as well as via two intracellular stores ('extended two-Ca-store concept').
1 - 4微摩尔/升的异丙肾上腺素浓度，在豚鼠右心室乳头肌和酶解分离的心肌细胞中均会引发一种钙超载诱导状态，在兴奋 - 收缩偶联过程中，其功能特征分别为双相（多相）抽搐和双相（多相）细胞内钙瞬变。在体外实验中，通过协调刺激间隔、灌流液温度以及添加钙激动剂，这种状态可稳定数小时。功能稳定性是实验结果可重复性的前提条件，尤其是在应用持久刺激程序之后。使用三种不同类型的操作，将双相收缩形状的变化与双相细胞内钙瞬变时间进程的变化进行了比较：（1）稳定起搏节律的中断；（2）刺激间隔的变化；（3）添加ryanodine。结果表明：（1）钙超载多细胞制剂中的鲍迪奇阶梯发生了变化，即抽搐的每个单独成分都经历了自身的阶梯。在双相细胞内钙瞬变的相位和张力成分的构型中可观察到类似行为。（2）在不同驱动频率下，双相抽搐的两个成分的相对比例与双相细胞内钙瞬变的两个成分的时间积分相对应。（3）Ryanodine抑制双相抽搐的第一个成分以及双相细胞内钙瞬变的相位成分。SR Ca(2 +)-ATP酶抑制剂毒胡萝卜素增加双相钙瞬变的第二个成分。这支持了以下假设，即张力成分的大小部分由细胞内钙再摄取决定。两种实验结果均与以下假设相符，即在钙超载的哺乳动物心脏细胞中，钙直接到达收缩系统以及通过两个细胞内储存库（“扩展的双钙储存概念”）。
