Cation permeation through the voltage-dependent potassium channel in the squid axon. Characteristics and mechanisms

P. K. Wagoner, G. S. Oxford

Research output: Contribution to journalArticle

36 Citations (Scopus)

Abstract

Characteristics of cation permeation through voltage-dependent delayed rectifier K channels in squid giant axons were examined. Axial wire voltage-clamp measurements and internal perfusion were used to determine conductance and permeability properties. These K channels exhibit conductance saturation and decline with increases in symmetrical K+ concentrations to 3 M. They also produce ion- and concentration-dependent current-voltage shapes. K channel permeability ratios obtained with substitutions of internal Rb+ or NH4+ for K+ are higher than for external substitution of these ions. Furthermore, conductance and permeability ratios of NH4+ or Rb+ to K+ are functions of ion concentration. Conductance measurements also reveal the presence of an anomalous mole fraction effect for NH4+, Rb+, or Tl+ to K+. Finally, internal Cs+ blocks these K channels in a voltrage-dependent manner, with relief of block by elevations in external K+ but not external NH4+ or Cs+. Energy profiles for K+, NH4+, Rb+, Tl+, and Cs+ incorporating three barriers and two ion-binding sites are fitted to the data. The profiles are asymmetric with respect to the center of the electric field, have different binding energies and electrical positions for each ion, and (for K+) exhibit concentration-dependent barrier positions.

Original languageEnglish (US)
Pages (from-to)261-290
Number of pages30
JournalJournal of General Physiology
Volume90
Issue number2
StatePublished - 1987
Externally publishedYes

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Decapodiformes
Potassium Channels
Axons
Cations
Ions
Permeability
Perfusion
Binding Sites

ASJC Scopus subject areas

  • Physiology

Cite this

Cation permeation through the voltage-dependent potassium channel in the squid axon. Characteristics and mechanisms. / Wagoner, P. K.; Oxford, G. S.

In: Journal of General Physiology, Vol. 90, No. 2, 1987, p. 261-290.

Research output: Contribution to journalArticle

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N2 - Characteristics of cation permeation through voltage-dependent delayed rectifier K channels in squid giant axons were examined. Axial wire voltage-clamp measurements and internal perfusion were used to determine conductance and permeability properties. These K channels exhibit conductance saturation and decline with increases in symmetrical K+ concentrations to 3 M. They also produce ion- and concentration-dependent current-voltage shapes. K channel permeability ratios obtained with substitutions of internal Rb+ or NH4+ for K+ are higher than for external substitution of these ions. Furthermore, conductance and permeability ratios of NH4+ or Rb+ to K+ are functions of ion concentration. Conductance measurements also reveal the presence of an anomalous mole fraction effect for NH4+, Rb+, or Tl+ to K+. Finally, internal Cs+ blocks these K channels in a voltrage-dependent manner, with relief of block by elevations in external K+ but not external NH4+ or Cs+. Energy profiles for K+, NH4+, Rb+, Tl+, and Cs+ incorporating three barriers and two ion-binding sites are fitted to the data. The profiles are asymmetric with respect to the center of the electric field, have different binding energies and electrical positions for each ion, and (for K+) exhibit concentration-dependent barrier positions.

AB - Characteristics of cation permeation through voltage-dependent delayed rectifier K channels in squid giant axons were examined. Axial wire voltage-clamp measurements and internal perfusion were used to determine conductance and permeability properties. These K channels exhibit conductance saturation and decline with increases in symmetrical K+ concentrations to 3 M. They also produce ion- and concentration-dependent current-voltage shapes. K channel permeability ratios obtained with substitutions of internal Rb+ or NH4+ for K+ are higher than for external substitution of these ions. Furthermore, conductance and permeability ratios of NH4+ or Rb+ to K+ are functions of ion concentration. Conductance measurements also reveal the presence of an anomalous mole fraction effect for NH4+, Rb+, or Tl+ to K+. Finally, internal Cs+ blocks these K channels in a voltrage-dependent manner, with relief of block by elevations in external K+ but not external NH4+ or Cs+. Energy profiles for K+, NH4+, Rb+, Tl+, and Cs+ incorporating three barriers and two ion-binding sites are fitted to the data. The profiles are asymmetric with respect to the center of the electric field, have different binding energies and electrical positions for each ion, and (for K+) exhibit concentration-dependent barrier positions.

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