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The Journal of Membrane Biology

, Volume 67, Issue 1, pp 91–98 | Cite as

Ion selectivity of the apical membrane Na channel in the toad urinary bladder

  • Lawrence G. Palmer
Article

Summary

The ion selectivity of the apical membrane Na channel in the toad urinary bladder was investigated. The electrical potential difference and resistance across the basal-lateral membrane were reduced using high concentrations of KCl in the serosal bathing medium, and gradients for various ions were imposed across the apical membrane by altering the composition of the mucosal bathing medium. Ion fluxes through the channel were measured as the transepithelial current inhibited by amiloride, a specific blocker of the channel's Na conductance. The selectivity sequence for alkali metal cations was H>Li>Na≫K. K, permeability was barely detectable; the selectivity for Na over K was about 1000:1. Ammonium, hydroxyl ammonium and hydrazinium ions were, like K, virtually impermeant. The results suggest that the size of the unhydrated ion is an important factor in determining permeability in this channel.

Key words

epithelial Na transport toad urinary bladder apical membrane ion selectivity Na channels 

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Copyright information

© Springer-Verlag New York Inc. 1982

Authors and Affiliations

  • Lawrence G. Palmer
    • 1
    • 2
  1. 1.Department of BiochemistryColumbia University College of Physicians and SurgeonsNew York
  2. 2.Department of PhysiologyCornell University Medical CollegeNew York

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