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Related Experiment Videos

Increase vs. decrease of calcium uptake by isolated heart cells induced by H2O2 vs. HOCl.

T Kaminishi1, T Matsuoka, T Yanagishita

  • 1Department of Physiology, University of Ottawa, School of Medicine, Ontario, Canada.

The American Journal of Physiology
|March 1, 1989
PubMed
Summary

Hydrogen peroxide (H2O2) increases intracellular calcium in heart cells by affecting sodium-calcium exchange. Hypochlorous acid (HOCl) decreases calcium content by inhibiting the sarcoplasmic reticulum calcium pump.

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Area of Science:

  • Cardiovascular Physiology
  • Cellular Biology
  • Biochemistry

Background:

  • Intracellular calcium (Ca2+) regulation is critical for cardiac function.
  • Oxidative stress, induced by reactive oxygen species like hydrogen peroxide (H2O2) and hypochlorous acid (HOCl), can disrupt cellular processes.
  • The precise mechanisms by which H2O2 and HOCl affect myocyte Ca2+ handling are not fully elucidated.

Purpose of the Study:

  • To investigate the distinct effects of H2O2 and HOCl on intracellular Ca2+ content in adult rat heart myocytes.
  • To elucidate the underlying mechanisms responsible for H2O2- and HOCl-induced alterations in myocyte Ca2+ homeostasis.

Main Methods:

  • Adult rat heart myocytes were loaded with radioactive calcium ([45Ca2+]).
  • Effects of H2O2 and HOCl on intracellular Ca2+ content, Na+-K+-ATPase activity ([3H]ouabain binding), and Ca2+ efflux were measured.

Related Experiment Videos

  • Experiments utilized myocyte permeabilization and isolated sarcoplasmic reticulum (SR) fractions to assess intracellular Ca2+ uptake and Ca2+-ATPase activity.

    • Main Results:

    • H2O2 significantly increased rapidly exchangeable intracellular Ca2+ by twofold, dependent on Na+, pH, and temperature, but not on L-type calcium channel blockers.
    • H2O2 inhibited Na+-K+-ATPase, leading to increased intracellular Na+ and subsequent Na+-Ca2+ exchange-mediated Ca2+ influx.
    • HOCl decreased intracellular Ca2+ content, accelerated Ca2+ efflux, and inhibited SR Ca2+ uptake and Ca2+-ATPase activity, effects antagonized by dithiothreitol.

    Conclusions:

    • H2O2 elevates intracellular Ca2+ in myocytes primarily by inhibiting the Na+-K+-ATPase, thereby stimulating Na+-Ca2+ exchange.
    • HOCl impairs myocyte Ca2+ handling by directly inhibiting the sarcoplasmic reticulum Ca2+ pump, leading to reduced Ca2+ content and enhanced efflux.
    • These findings differentiate the mechanisms of Ca2+ dysregulation by H2O2 and HOCl in cardiac myocytes, highlighting distinct targets of oxidative stress.