A quantitative description of membrane current and its application to conduction and excitation in nerve

Abstract

This article concludes a series of papers concerned with the flow of electric current through the surface membrane of a giant nerve fibre (Hodgkin, Huxley & Katz, 1952; Hodgkin & Huxley, 1952 a-c). Its general object is to discu the results of the preceding papers (Part I), to put them into mathematical form (Part II) and to show that they will account for conduction and excitation in quantitative terms (Part III).PART I. DISCUSSION OF EXPERIMENTAL RESULTS The results described in the preceding papers suggest that the electrical behaviour of the membrane may be represented by the network shown in Fig. 1. Current can be carried through the membrane either by charging the membrane capacity or by movement of ion-s through the resistances in parallel with the capacity. The ionic current is divided into components carried by sodium and potassium ions (INa and IK), and a small 'leakage current' (I,) made up by chloride and other ions. Each component of the ionic current is determined by a driving force which may conveniently be measured as an electrical potential difference and a permeability coefficient which has the dimensions of a conductance. Thus the sodium current (INa) is equal to the sodium conductance (9Na) multiplied by the difference between the membrane potential (E) and the equilibrium potential for the sodium ion (ENa). Similar equations apply to 'K and I, and are collected on p. 505.Our experiments suggest that gNa and 9E are functions of time and membrane potential, but that ENa, EK, El, CM and g, may be taken as constant. The influence of membrane potential on permeability can be summarized by stating: first, that depolarization causes a transient increase in sodium conductance and a slower but maintained increase in potassium conductance; secondly, that these changes are graded and that they can be reversed by repolarizing the membrane. In order to decide whether these effects are sufficient to account for complicated phenomena such as the action potential and refractory period, it is necessary to obtain expressions relating

Potassium channels expressed from rat brain cDNA have delayed rectifier properties

“…These channels are highly selective for K ÷ and the macroscopic currents mediated by these channels have time courses resembling those of the classical, delayed outward K + currents described for nerve and muscle [16,17]. The properties of single RCK1 channels are not completely homogeneous; they can adopt multiple-conductance states and switch between different gating modes.…”

Two‐Pore K + Channel TREK‐1 Regulates Sinoatrial Node Membrane Excitability

“…The importance of background (“leak”) K + channels for excitable cell function has been known for the better part of a century 1. Despite the central role of these channels in maintaining normal membrane excitability in a wide variety of cells, including cardiac myocytes,2 our knowledge of their specific identity and physiological functions lags behind that of other K + channel families (eg, voltage‐dependent and inward rectifier K + channels), in part because of the lack of specific pharmacological agents and animal models.…”

Solutions of the Hodgkin‐huxley Equations for Squid Axon Treated With Tetraethylammonium and in Potassium‐rich Media

“…cm.~" msec.~Ŵ e have therefore modified the Hodgkin-Huxley equations (Hodgkin and Huxley, 1952) in such a manner as to comply with these experimental conditions. For the membrane action potential the equations to be solved may be written in the well-known form (Hodgkin and Huxley, 1952).…”