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Author Notes:

Correspondence to Peter H. Backx: p.backx@utoronto.ca

David C. Gadsby served as editor.

We thank L.Y. Jan for providing us with the Kir2.1 clone and A. Prendergast for his technical assistance.

Subjects:

Research Funding:

This study was supported by Heart and Stroke Foundation of Ontario (grant T-4179) to P.H. Backx. P.H. Backx is a Career Investigator of the Heart and Stroke Foundation of Ontario.

H.C. Cho was supported by a Canadian Institutes of Health Research studentship. N. D'Avanzo holds a studentship from Heart & Stroke Richard Lewar Center of Excellence at the University of Toronto.

Keywords:

  • Science & Technology
  • Life Sciences & Biomedicine
  • Physiology
  • surface charges
  • Kir2.1
  • conduction
  • NMG
  • TMO
  • ACETYLCHOLINE-RECEPTOR CHANNEL
  • CA-2+-ACTIVATED K+ CHANNEL
  • SURFACE-CHARGE
  • ION CONDUCTION
  • HEART-FAILURE
  • SODIUM-CHANNELS
  • CHEMICAL MODIFICATION
  • SUPEROXIDE-DISMUTASE
  • VENTRICULAR MYOCYTES
  • POISSON-BOLTZMANN

Conduction through the inward rectifier potassium channel, Kir2.1, is increased by negatively charged extracellular residues

Tools:

Journal Title:

Journal of General Physiology

Volume:

Volume 125, Number 5

Publisher:

, Pages 493-503

Type of Work:

Article | Final Publisher PDF

Abstract:

Ion channel conductance can be influenced by electrostatic effects originating from fixed "surface" charges that are remote from the selectivity filter. To explore whether surface charges contribute to the conductance properties of Kir2.1 channels, unitary conductance was measured in cell-attached recordings of Chinese hamster ovary (CHO) cells transfected with Kir2.1 channels over a range of K + activities (4.6-293.5 mM) using single-channel measurements as well as nonstationary fluctuation analysis for low K + activities. K + ion concentrations were shown to equilibrate across the cell membrane in our studies using the voltage-sensitive dye DiBAC 4 (5). The dependence of γ on the K + activity (a K ) was fit well by a modified Langmuir binding isotherm, with a nonzero intercept as a K approaches 0 mM, suggesting electrostatic surface charge effects. Following the addition of 100 mM N-methyl-D-glucamine (NMG + ), a nonpermeant, nonblocking cation or following pretreatment with 50 mM trimethyloxonium (TMO), a carboxylic acid esterifying agent, the γ-a K relationship did not show nonzero intercepts, suggesting the presence of surface charges formed by glutamate or aspartate residues. Consistent with surface charges in Kir2.1 channels, the rates of current decay induced by Ba 2+ block were slowed with the addition of NMG or TMO. Using a molecular model of Kir2.1 channels, three candidate negatively charged residues were identified near the extracellular mouth of the pore and mutated to cysteine (E125C, D152C, and E153C). E153C channels, but not E125C or D152C channels, showed hyperbolic γ-a K relationships going through the origin. Moreover, the addition of MTSES to restore the negative charges in E53C channels reestablished wild-type conductance properties. Our results demonstrate that E153 contributes to the conductance properties of Kir2.1 channels by acting as a surface charge.

Copyright information:

© 2005, The Rockefeller University Press

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