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Related Experiment Videos

Paracellular ion channel at the tight junction.

Vivian W Tang1, Daniel A Goodenough

  • 1Department of Cell Biology, Harvard Medical School, 240 Longwood Ave., Boston, Massachusetts 02115, USA.

Biophysical Journal
|March 1, 2003
PubMed
Summary

Epithelial tight junctions allow ion passage through novel channels, not just pores. These paracellular-tight junction channels (PTJC) exhibit ion channel properties and facilitate extracellular ion transport.

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Area of Science:

  • Cell Biology
  • Biophysics
  • Physiology

Background:

  • Epithelial tight junctions regulate paracellular permeability, excluding macromolecules while allowing ion passage.
  • The mechanism of ion permeation through tight junctions (aqueous pores vs. ion channels) remains unclear.

Purpose of the Study:

  • To investigate the biophysical properties of ion permeation across epithelial tight junctions.
  • To determine if tight junctions contain discrete ion channels mediating extracellular ion transport.

Main Methods:

  • Development of paracellular ion flux assays for extracellular ions (Na+, Cl-, Ca2+, Mg2+).
  • Analysis of tight junction permeability based on ion concentration, competition, and pH sensitivity.

Main Results:

  • Tight junctions exhibit ion channel-like properties: size/charge selectivity, concentration-dependent permeability, competitive inhibition, anomalous mole-fraction effects, and pH sensitivity.
  • Evidence supports the presence of discrete ion channels within the tight junction.
  • These channels, termed paracellular-tight junction channels (PTJC), are oriented parallel to plasma membranes.

Conclusions:

  • The tight junction facilitates paracellular ion transport via a novel class of ion channels (PTJC).
  • PTJC represent a distinct mechanism for regulating ion flux between extracellular compartments.

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