Lewartowski B, Rózycka M, Janiak R
Department of Clinical Physiology, Medical Center of Postgraduate Education, Warsaw, Poland.
Am J Physiol. 1994 May;266(5 Pt 2):H1829-39. doi: 10.1152/ajpheart.1994.266.5.H1829.
We compared the effects of thapsigargin (TG), a selective blocker of Ca(2+)-adenosinetriphosphatase of sarcoplasmic reticulum (SR), and ryanodine (Ry) in the single isolated myocytes of guinea pig ventricular myocardium loaded with indo 1 acetoxymethyl ester (AM). TG (2 x 10(-7) M) inhibited the rapid phase of Ca2+ transient, increased time to peak intracellular Ca2+ concentration ([Ca2+]i) from 158 +/- 12 to 391 +/- 60 ms and decreased the total amplitude of the transient to 89 +/- 4% of the pre-TG control. Time to peak of contractions increased from 350 +/- 47 to 410 +/- 37 ms and total duration from 666 +/- 62 to 850 +/- 198 ms. Total amplitude of contractions was hardly affected. In the cells not loaded with indo 1-AM TG decreased the amplitude of contractions to 71 +/- 3% of control. When the effects of TG were fully developed, the cells ceased to respond to 1 s of superfusion with 15.0 mM caffeine with transient elevation of [Ca2+]i and/or transient contracture. TG did not affect the amplitude or time course of Ca2+ current (ICa) or the current-voltage relation. We propose that Ca2+ transients and contractions in the cells treated with TG were initiated by sarcolemmal Ca2+ influx. Ry (1.0 microM) initiated similar changes in the time course of Ca2+ transients and contractions as TG; however, total amplitude of the transients and contractions was reduced to 78 +/- 5 and 55 +/- 7% of the control, respectively. The SR Ca2+ was also depleted by Ry. TG superfused over the cells pretreated with Ry increased the amplitude of Ca2+ transients and respective contractions to the pre-Ry level. TG did not affect the ICa in the cells pretreated with Ry nor did it change configuration of action potentials to increase the Ca2+ influx. We propose that the effect of Ry on amplitude of Ca2+ transients and contractions results from the trapping of a fraction of sarcolemmal Ca2+ influx by the SR and its rapid release into subsarcolemmal space. From there it is extruded out of the cell by Na(+)-Ca2+ exchange before ever reaching the contractile system.
我们比较了毒胡萝卜素（TG）和ryanodine（Ry）对负载indo 1乙酰氧基甲酯（AM）的豚鼠心室肌单个分离心肌细胞的影响。TG是肌浆网（SR）的Ca(2+)-三磷酸腺苷酶的选择性阻滞剂。TG（2×10(-7) M）抑制了Ca2+瞬变的快速相，使细胞内Ca2+浓度（[Ca2+]i）达到峰值的时间从158±12毫秒增加到391±60毫秒，并使瞬变的总幅度降低到TG处理前对照的89±4%。收缩达到峰值的时间从350±47毫秒增加到410±37毫秒，总持续时间从666±62毫秒增加到850±198毫秒。收缩的总幅度几乎没有受到影响。在未负载indo 1-AM的细胞中，TG将收缩幅度降低到对照的71±3%。当TG的作用充分发挥时，细胞对用15.0 mM咖啡因进行1秒的灌流不再有反应，即[Ca2+]i不再有短暂升高和/或不再有短暂挛缩。TG不影响Ca2+电流（ICa）的幅度或时间进程，也不影响电流-电压关系。我们认为，用TG处理的细胞中的Ca2+瞬变和收缩是由肌膜Ca2+内流引发的。Ry（1.0 microM）在Ca2+瞬变和收缩的时间进程中引发了与TG类似的变化；然而，瞬变和收缩的总幅度分别降低到对照的78±5%和55±7%。SR中的Ca2+也被Ry耗尽。用Ry预处理过的细胞再用TG灌流，可使Ca2+瞬变和相应收缩的幅度增加到Ry处理前的水平。TG不影响用Ry预处理过的细胞中的ICa，也不改变动作电位的形态以增加Ca2+内流。我们认为，Ry对Ca2+瞬变和收缩幅度的影响是由于SR捕获了一部分肌膜Ca2+内流，并将其快速释放到肌膜下空间。从那里，它在到达收缩系统之前就通过Na(+)-Ca2+交换被挤出细胞。
