The relative permeability of sodium channels to eight metal cations is studied in myelinated nerve fibers. Ionic currents under voltage-clamp conditions are measured in Na-free solutions containing the test ion. Measured reversal potentials and the Goldman equation are used to calculate the permeability sequence: Na+ ≈ Li+ > Tl+ > K+. The ratio PK/PNa is 1/12. The permeabilities to Rb+, Cs+, Ca++, and Mg++ are too small to measure. The permeability ratios agree with observations on the squid giant axon and show that the reversal potential ENa differs significantly from the Nernst potential for Na+ in normal axons. Opening and closing rates for sodium channels are relatively insensitive to the ionic composition of the bathing medium, implying that gating is a structural property of the channel rather than a result of the movement or accumulation of particular ions around the channel. A previously proposed pore model of the channel accommodates the permeant metal cations in a partly hydrated form. The observed sequence of permeabilities follows the order expected for binding to a high field strength anion in Eisenman's theory of ion exchange equilibria.
Article|
June 01 1972
The Permeability of the Sodium Channel to Metal Cations in Myelinated Nerve
Bertil Hille
Bertil Hille
From the Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195
Search for other works by this author on:
Bertil Hille
From the Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195
Received:
December 16 1971
Online ISSN: 1540-7748
Print ISSN: 0022-1295
Copyright © 1972 by The Rockefeller University Press
1972
J Gen Physiol (1972) 59 (6): 637–658.
Article history
Received:
December 16 1971
Citation
Bertil Hille; The Permeability of the Sodium Channel to Metal Cations in Myelinated Nerve . J Gen Physiol 1 June 1972; 59 (6): 637–658. doi: https://doi.org/10.1085/jgp.59.6.637
Download citation file: