Pizarro G, Cleemann L, Morad M
Proc Natl Acad Sci U S A. 1985 Mar;82(6):1864-8. doi: 10.1073/pnas.82.6.1864.
Sarcolemmal Ca2+ movements in frog ventricular strips were measured by monitoring Ca2+ depletion from the extracellular space with an impermeant Ca indicator dye, antipyrylazo III. Ca2+ depletion was measured as a weighted average of light signals recorded simultaneously at three different wavelengths. This weighting procedure was designed to reduce the motion-induced light scattering and to enhance the Ca2+-related optical signals. Comparison of the time course of Ca2+ depletion signal with that of contraction showed that the rate of Ca2+ depletion was maximal immediately after the upstroke of the action potential but prior to the onset of tension. Peak Ca2+ depletion was reached toward the end of the action potential and amounted to a 10-50 microM decrease in the total extracellular Ca2+ concentration. The reaccumulation of extracellular Ca2+ seen after the action potential was 2-5 sec slower than the relaxation of tension. The rate of Ca2+ depletion had a bell-shaped voltage dependence and was enhanced by epinephrine, suggesting that Ca2+ influx occurred primarily through a slowly inactivating ionic channel. Ca2+ transport through the Na+-Ca2+ exchange system was not significantly altered in the presence of strophanthidin or with decrease of extracellular K+ concentration despite marked potentiation of tension by these agents. Ca2+ depletion measured at the end of a 1-sec clamp pulse had a voltage dependence noticeably different from that of the developed tension. This finding may suggest that a fraction of activator Ca2+ is released from membrane-bound Ca2+ pools in a voltage-dependent manner. Our results show that Ca2+ indicator dyes can be used not only to measure rapid changes in the extracellular Ca2+ concentration during contraction, but also to quantify the contribution of various sarcolemmal Ca2+ transport systems to the generation of tension in cardiac muscle.
通过使用不透性钙指示剂染料安替比拉宗III监测细胞外空间的钙消耗，来测量青蛙心室肌条中肌膜的钙离子运动。钙消耗以在三个不同波长同时记录的光信号的加权平均值来测量。这种加权程序旨在减少运动引起的光散射，并增强与钙相关的光信号。将钙消耗信号的时间进程与收缩的时间进程进行比较，结果表明，钙消耗速率在动作电位上升支之后但在张力开始之前立即达到最大值。在动作电位接近结束时达到钙消耗峰值，导致细胞外总钙浓度下降10 - 50微摩尔。动作电位后观察到的细胞外钙的重新积累比张力松弛慢2 - 5秒。钙消耗速率具有钟形电压依赖性，并被肾上腺素增强，这表明钙内流主要通过一个缓慢失活的离子通道发生。尽管毒毛花苷或细胞外钾浓度降低会显著增强张力，但通过钠钙交换系统的钙转运在这些情况下并没有明显改变。在1秒钳制脉冲结束时测量的钙消耗具有与所产生张力明显不同的电压依赖性。这一发现可能表明，一部分激活钙以电压依赖性方式从膜结合钙库中释放。我们的结果表明，钙指示剂染料不仅可用于测量收缩过程中细胞外钙浓度的快速变化，还可用于量化各种肌膜钙转运系统对心肌张力产生的贡献。
