Inoue Masashi, Bridge John H B
Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, 95 South 2000 East, Salt Lake City, UT 84112-5000, USA.
Biophys J. 2005 Nov;89(5):3102-10. doi: 10.1529/biophysj.105.065862. Epub 2005 Aug 19.
Variation in couplon size is thought to be essential for graded Ca(2+) transients in cardiac myocytes. We examined this variation by investigating spark appearance in rabbit ventricular myocytes at various locations and at potentials from -20 to 0 mV. At 0 mV, sparks appeared at the beginning of the voltage step with a probability of unity. On the other hand, at -20 mV, sparks appeared later during the voltage step with a lower probability. The cumulative spark probabilities at various potentials were fitted with exponential functions of both time and voltage. Spark latency became longer as spark probability decreased at more negative potentials. At -20 mV, the cumulative spark probability and the mean spark latency were not only variable among locations but also inversely related. Under the assumption that a single opening of an L-type Ca(2+) channel triggers a spark, we suggest a simple mathematical explanation for the distribution of spark appearance. The variation in spark probability and latency with location suggests that the couplon size, and hence the number of L-type Ca(2+) channels in a couplon is variable.
偶联子大小的变化被认为是心肌细胞中分级钙瞬变的关键因素。我们通过研究兔心室肌细胞在不同位置以及-20至0 mV电位下的钙火花出现情况来检测这种变化。在0 mV时，电压阶跃开始时钙火花出现的概率为1。另一方面，在-20 mV时，钙火花在电压阶跃后期出现，概率较低。不同电位下的累积钙火花概率可用时间和电压的指数函数拟合。在更负的电位下，随着钙火花概率降低，钙火花潜伏期变长。在-20 mV时，累积钙火花概率和平均钙火花潜伏期不仅在不同位置之间存在差异，而且呈负相关。假设单个L型钙通道的开放触发一个钙火花，我们提出了一个关于钙火花出现分布的简单数学解释。钙火花概率和潜伏期随位置的变化表明偶联子大小，进而偶联子中L型钙通道的数量是可变的。
