Djamgoz M B, Dawson J
Department of Pure and Applied Biology, Imperial College, London.
J Exp Biol. 1988 May;136:433-49. doi: 10.1242/jeb.136.1.433.
A model of resting membrane electrogenesis in skeletal muscles of prepupal Calliphora erythrocephala was formulated. From experiments in which reversible effects of changing extracellular K+ and Na+ activities on the membrane potential (EM) were measured, three different values of alpha (the ratio of the partial permeabilities of the membrane to Na+ and K+) were derived, each from a different range of extracellular Na+ and K+ activities. Two independent tests were carried out to determine the most realistic value of alpha. Intracellular K+ and Na+ activities and EM values were measured in a population of cells, and the EM values predicted using the Goldman-Hodgkin-Katz equation for different values of alpha. The best fit for the data was obtained for alpha = 0.036. In ionic substitution experiments, in which passive movements of Cl- were prevented or minimized, the changes in EM around the resting level could be explained with a high degree of accuracy by assuming again that alpha = 0.036. However, tests of the model by investigation of direct effects of reducing extracellular Na+ concentration over a wide range of EM values gave an anomalous result. In low-Na+ Ringer, EM values became more positive than the respective resting levels. The anomalous effect of low-Na+ Ringer on EM did not involve a change in the K+ equilibrium potential. Instead, it was probably due to a reduction in the K+ permeability of the membrane. Possible mechanisms underlying this effect are discussed.
构建了红头丽蝇蛹前期骨骼肌静息膜电发生的模型。通过测量改变细胞外钾离子（K⁺）和钠离子（Na⁺）活性对膜电位（EM）的可逆影响的实验，得出了三个不同的α值（膜对Na⁺和K⁺的部分渗透率之比），每个值都来自不同范围的细胞外Na⁺和K⁺活性。进行了两项独立测试以确定最符合实际的α值。在一群细胞中测量细胞内K⁺和Na⁺活性以及EM值，并使用戈德曼-霍奇金- Katz方程针对不同的α值预测EM值。当α = 0.036时，数据拟合最佳。在离子替代实验中，其中氯离子（Cl⁻）的被动移动被阻止或最小化，通过再次假设α = 0.036，可以高度准确地解释静息水平附近EM的变化。然而，通过在广泛的EM值范围内研究降低细胞外Na⁺浓度的直接影响来测试该模型，得到了一个异常结果。在低钠林格氏液中，EM值变得比各自的静息水平更正。低钠林格氏液对EM的异常影响不涉及K⁺平衡电位的变化。相反，这可能是由于膜的K⁺通透性降低所致。讨论了这种效应背后的可能机制。
