Pollard J R, Arispe N, Rojas E, Pollard H B
Laboratory of Cell Biology and Genetics, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Biophys J. 1994 Aug;67(2):647-55. doi: 10.1016/S0006-3495(94)80525-9.
Ion channels can express multiple conductance levels that are not integer multiples of some unitary conductance, and that interconvert among one another. We report here that for 26 different types of multiple conductance channels, all allowed conductance levels can be calculated accurately using the geometric sequence gn = g(o) (3/2)n, where gn is a conductance level and n is an integer > or = 0. We refer to this relationship as the "3/2 Rule," because the value of any term in the sequence of conductances (gn) can be calculated as 3/2 times the value of the preceding term (gn-1). The experimentally determined average value for "3/2" is 1.491 +/- 0.095 (sample size = 37, average +/- SD). We also verify the choice of a 3/2 ratio on the basis of error analysis over the range of ratio values between 1.1 and 2.0. In an independent analysis using Marquardt's algorithm, we further verified the 3/2 ratio and the assignment of specific conductances to specific terms in the geometric sequence. Thus, irrespective of the open time probability, the allowed conductance levels of these channels can be described accurately to within approximately 6%. We anticipate that the "3/2 Rule" will simplify description of multiple conductance channels in a wide variety of biological systems and provide an organizing principle for channel heterogeneity and differential effects of channel blockers.
离子通道能够表达多种电导水平，这些电导水平并非某个单一电导的整数倍，且它们之间可以相互转换。我们在此报告，对于26种不同类型的多电导通道，所有允许的电导水平都可以使用几何序列gn = g(o) (3/2)n精确计算，其中gn是一个电导水平，n是大于或等于0的整数。我们将这种关系称为“3/2规则”，因为电导序列（gn）中任何一项的值都可以计算为前一项（gn-1）值的3/2倍。“3/2”的实验测定平均值为1.491 +/- 0.095（样本量 = 37，平均值 +/- 标准差）。我们还基于在1.1至2.0之间的比值范围内的误差分析，验证了3/2比值的选择。在使用Marquardt算法的独立分析中，我们进一步验证了3/2比值以及将特定电导分配给几何序列中的特定项。因此，无论开放时间概率如何，这些通道允许的电导水平都可以精确到约6%以内进行描述。我们预计“3/2规则”将简化对多种生物系统中多电导通道的描述，并为通道异质性和通道阻滞剂的不同效应提供一个组织原则。
