Voltage dependence of the pattern and frequency of discrete Ca2+ release events after brief repriming in frog skeletal muscle
Voltage dependence of the pattern and frequency of discrete Ca2+ release events after brief repriming in frog skeletal muscle
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DOI：
10.1073/pnas.94.20.11061
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发表时间：
1997-09-30
影响因子：
11.1
通讯作者：
Schneider, MF
中科院分区：
文献类型：
--
作者：
Klein, MG;Lacampagne, A;Schneider, MF
对去极化的蛙骨骼肌纤维施加短暂的复极化预脉冲，可使一小部分横小管膜电压传感器从失活状态恢复。在随后的去极化测试脉冲期间，我们检测到肌浆Ca ~（2+）浓度短暂、高度局部化的升高（Ca 2+“火花”）在所有测试脉冲电压下由单个三元组中的恢复电压传感器引发，这些事件的潜伏期直方图给出了由恢复的电压传感器控制的肌浆网（SR）钙释放通道的门控模式。事件频率和在测试脉冲开始附近的事件的聚集两者都随着测试脉冲去极化而增加，宏观SR钙释放波形，从火花潜伏期直方图和估计的开放时间的通道或通道下的火花，表现出早期的峰值和快速显着下降，在大的去极化。对于较小的去极化，释放波形表现出较小的峰值和较慢的下降。然而，在所有测试去极化和在给定去极化期间的所有时间，单个火花的平均使用时间和平均幅度非常相似，这表明火花下的通道开放时间和电导基本上与电压无关。因此，SRCa 2+释放的电压依赖性是由于个体的、电压无关的、离散的释放事件的发生频率和模式的变化。
Applying a brief repolarizing pre-pulse to a depolarized frog skeletal muscle fiber restores a small fraction of the transverse tubule membrane voltage sensors from the inactivated state, During a subsequent depolarizing test pulse we detected brief, highly localized elevations of myoplasmic Ca2+ concentration (Ca2+ ''sparks'') initiated by restored voltage sensors in individual triads at all test pulse voltages, The latency histogram of these events gives the gating pattern of the sarcoplasmic reticulum (SR) calcium release channels controlled by the restored voltage sensors, Both event frequency and clustering of events near the start of the test pulse increase with test pulse depolarization, The macroscopic SR calcium release waveform, obtained from the spark latency histogram and the estimated open time of the channel or channels underlying a spark, exhibits an early peak and rapid marked decline during large depolarizations. For smaller depolarizations, the release waveform exhibits a smaller peak and a slower decline, However, the mean use time and mean amplitude of the individual sparks are quite similar at all test depolarizations and at all times during a given depolarization, indicating that the channel open times and conductances underlying sparks are essentially independent of voltage, Thus, the voltage dependence of SR Ca2+ release is due to changes in the frequency and pattern of occurrence of individual, voltage-independent, discrete release events.