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Related Experiment Videos

Activation of Na+/H+ exchange is required for regulatory volume decrease after modest "physiological" volume

R J MacLeod1, J R Hamilton

  • 1Department of Pediatrics, McGill University, Montreal Children's Hospital Research Institute, Montreal, Quebec H3H 1P3, Canada.

The Journal of Biological Chemistry
|September 20, 1996
PubMed
Summary

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Regulatory volume decrease (RVD) in jejunal villus cells involves Na+/H+ exchange (NHE). NHE-1 activation by modest cell swelling, driven by Na+ absorption, is crucial for RVD and subsequent alkalinization, facilitating osmolyte loss.

Area of Science:

  • Cellular physiology
  • Ion transport mechanisms
  • Gastrointestinal biology

Background:

  • Epithelial cells regulate volume via ion transport following solute uptake or osmotic changes.
  • Regulatory volume decrease (RVD) involves K+ and Cl- channels.
  • The role of Na+/H+ exchange (NHE) in RVD of enterocytes requires further elucidation.

Purpose of the Study:

  • To investigate the relationship between Na+/H+ exchange (NHE) and regulatory volume decrease (RVD) in guinea pig jejunal villus cells.
  • To determine the specific NHE isoform involved in RVD following physiological cell swelling.
  • To assess the impact of varying hypotonicity on NHE activity and its role in RVD.

Main Methods:

  • Suspended guinea pig jejunal villus cells were used.

Related Experiment Videos

  • Cell volume changes were measured using electronic sizing.
  • Intracellular pH (pHi) was monitored using fluorescent spectroscopy.
  • Inhibitors of NHE, including 5-(N-methyl-N-isobutyl) amiloride (MIA), were employed.

    • Main Results:

    • Modest hypotonic dilution (5-7%) caused cell alkalinization, blocked by MIA, indicating NHE-1 involvement.
    • RVD following modest hypotonic dilution was inhibited by Na+-free medium and amiloride derivatives.
    • NHE activity was stimulated by 5% hypotonicity but inhibited by 30% hypotonicity, with NHE-1 being key for RVD after physiological swelling.
    • Complete volume regulation after swelling required alkalinization, mediated by NHE.

    Conclusions:

    • The NHE-1 isoform of Na+/H+ exchange is stimulated by physiological volume increases in Na+-absorbing enterocytes.
    • NHE-1 activation and subsequent pHi alkalinization are essential for the osmolyte loss driving RVD.
    • This mechanism represents a distinct volume regulatory pathway in intestinal epithelial cells.