Díaz M E, Cook S J, Chamunorwa J P, Trafford A W, Lancaster M K, O'Neill S C, Eisner D A
Department of Veterinary Preclinical Sciences, University of Liverpool, UK.
Circ Res. 1996 May;78(5):857-62. doi: 10.1161/01.res.78.5.857.
We have studied the factors responsible for the variation of the frequency of "waves" caused by spontaneous Ca2+ release in rat ventricular myocytes. The experiments were performed in isolated myocytes using the fluorescent indicators Indo-1 (to measure [Ca2+]i) and SBFI (to measure [Na+]i). After electrical stimulation (either with action potentials or voltage-clamp pulses), some cells showed spontaneous Ca2+ release. The frequency of this release, where present, was variable. The Ca2+ content of the sarcoplasmic reticulum (SR) was measured by applying caffeine (10 mmol/L). The resulting increase of [Ca2+]i activated the electrogenic Na(+)-Ca2+ exchange, and the integral of this current was used to estimate the Ca2+ content of the SR. The SR Ca2+ content was significantly higher in cells that oscillated at high rates ( > 10 . min-1) than in those that were quiescent. The rate of removal of Ca2+ from the cytoplasm by non-SR mechanisms was measured by adding caffeine (10 mmol/L) and measuring the rate constant of decay of the resulting increase of [Ca2+]i. Cells that had a high rate constant of decay of [Ca2+]i had a low frequency of oscillations. Measurements of [Na+]i showed a positive correlation between the frequency of spontaneous SR Ca2+ release and [Na+]i. After cessation of stimulation, there was a gradual decrease of [Na+]i, which was correlated with a parallel decrease of the frequency of oscillation rate. We conclude that the variability of frequency of spontaneous SR Ca2+ release is due to variations of the rate of Ca2+ removal from the cell, which are probably due to Na(+)-Ca2+ exchange. The variability of Na(+)- Ca2+ exchange rate, in turn, is likely to result from variations of [Na+]i.
我们研究了大鼠心室肌细胞中由自发Ca2+释放引起的“波”频率变化的相关因素。实验在分离的肌细胞中进行，使用荧光指示剂Indo-1（用于测量[Ca2+]i）和SBFI（用于测量[Na+]i）。电刺激（通过动作电位或电压钳脉冲）后，一些细胞出现自发Ca2+释放。这种释放的频率（若存在）是可变的。通过施加咖啡因（10 mmol/L）来测量肌浆网（SR）的Ca2+含量。由此导致的[Ca2+]i升高激活了生电性Na(+)-Ca2+交换，该电流的积分用于估计SR的Ca2+含量。在高频振荡（>10次/分钟）的细胞中，SR Ca2+含量显著高于静止细胞。通过添加咖啡因（10 mmol/L）并测量由此产生的[Ca2+]i升高的衰减速率常数，来测量非SR机制从细胞质中去除Ca2+的速率。[Ca2+]i衰减速率常数高的细胞振荡频率低。[Na+]i的测量显示，自发SR Ca2+释放频率与[Na+]i呈正相关。刺激停止后，[Na+]i逐渐降低，这与振荡频率的平行降低相关。我们得出结论，自发SR Ca2+释放频率的变化是由于细胞内Ca2+去除速率的变化，这可能是由于Na(+)-Ca2+交换所致。而Na(+)-Ca2+交换速率的变化反过来可能是由[Na+]i的变化引起的。
