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Related Experiment Videos

Cell membranes impermeable to NH3.

D Kikeri1, A Sun, M L Zeidel

  • 1Department of Medicine Brigham and Women's Hospital, Boston, Massachusetts.

Nature
|June 8, 1989
PubMed
Summary

Biological membranes typically allow small, neutral molecules to pass easily. However, this study reveals that kidney tubule cells are impermeable to ammonia (NH3) but permeable to ammonium (NH4+), challenging previous assumptions about ion transport.

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Area of Science:

  • Renal Physiology
  • Membrane Biology
  • Ion Transport

Background:

  • Cell membranes are generally more permeable to small, neutral molecules like ammonia (NH3) than charged species.
  • Ammonium (NH4+) distribution is traditionally attributed to NH3 diffusion and pH gradients.
  • This model assumes lipophilicity dictates membrane permeability.

Purpose of the Study:

  • To investigate the permeability of renal tubule cells to ammonia (NH3) and ammonium (NH4+).
  • To challenge the classical understanding of ion transport across biological membranes.
  • To develop a new model for ammonium transport in the kidney.

Main Methods:

  • Investigated the permeability of the apical membrane of medullary thick ascending limb of Henle cells.
  • Utilized a model incorporating novel membrane properties.
  • Analyzed the vectorial movement of NH4+ across epithelial cells.

Main Results:

  • Renal tubule cells exhibit an apical membrane virtually impermeable to ammonia (NH3).
  • These cells demonstrate high permeability to ammonium (NH4+).
  • A new model successfully explains NH4+ movement across compartments with equal pH.

Conclusions:

  • The apical membrane of medullary thick ascending limb of Henle cells possesses unique permeability characteristics.
  • These properties allow for direct NH4+ transport, independent of NH3 diffusion.
  • A revised understanding of renal ammonium handling is proposed, challenging classical models.

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