Strickholm A, Wallin B G
J Gen Physiol. 1967 Aug;50(7):1929-53. doi: 10.1085/jgp.50.7.1929.
The changes in membrane potential of isolated, single crayfish giant axons following rapid shifts in external ion concentrations have been studied. At normal resting potential the immediate change in membrane potential after a variation in external potassium concentration is quite marked compared to the effect of an equivalent chloride change. If the membrane is depolarized by a maintained potassium elevation, the immediate potential change due to a chloride variation becomes comparable to that of an equivalent potassium change. There is no appreciable effect on membrane potential when external sodium is varied, at normal or at a depolarized membrane potential. Starting from the constant field equation, expressions for the permeability ratios P(Cl)/P(K), P(Na)/P(K), and for intracellular potassium and chloride concentrations are derived. At normal resting membrane potential, P(Cl)/P(K) is 0.13 but at a membrane potential of -53 mv (external potassium level increased about five times) it is 0.85. The intracellular concentrations of potassium and chloride are estimated to be 233 and 34 mM, respectively, and it is pointed out that this is not compatible with ions distributed in a Nernst equilibrium across the membrane. It is also stressed that the information given by a plot of membrane potential vs. the logarithm of external potassium concentrations is very limited and rests upon several important assumptions.
对分离的单个小龙虾巨轴突在外部离子浓度快速变化后膜电位的变化进行了研究。在正常静息电位下，与等量氯化物变化的影响相比，外部钾浓度变化后膜电位的即时变化相当明显。如果膜因持续的钾升高而 depolarized，由于氯化物变化引起的即时电位变化变得与等量钾变化相当。当外部钠在正常或 depolarized 膜电位下变化时，对膜电位没有明显影响。从恒定场方程出发，推导出渗透率比P(Cl)/P(K)、P(Na)/P(K)以及细胞内钾和氯化物浓度的表达式。在正常静息膜电位下，P(Cl)/P(K)为0.13，但在膜电位为-53毫伏（外部钾水平增加约五倍）时，它为0.85。细胞内钾和氯化物的浓度估计分别为233和34毫摩尔，并且指出这与跨膜以能斯特平衡分布的离子不相符。还强调了膜电位与外部钾浓度对数的关系图所提供的信息非常有限，并且基于几个重要假设。
