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Related Experiment Videos

Correlation between relaxation and automaticity in embryonic heart cell aggregates.

W T Clusin

    Proceedings of the National Academy of Sciences of the United States of America
    |January 1, 1980
    PubMed
    Summary

    Cardiac muscle relaxation involves a slow phase linked to intracellular calcium removal, impacting pacemaker potential and muscle automaticity. This study reveals a connection between calcium dynamics and cardiac electrical activity.

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    Area of Science:

    • Cardiology
    • Cell Physiology
    • Biophysics

    Background:

    • Diastolic depolarization in cardiac muscle is linked to decreased potassium permeability.
    • This decrease is thought to be caused by the removal of intracellular free calcium.
    • A potential consequence is a continued decline in tension during the pacemaker potential.

    Purpose of the Study:

    • To investigate the relationship between intracellular calcium, cardiac muscle relaxation, and the pacemaker potential.
    • To characterize the phases of relaxation in chicken embryonic heart cell aggregates.
    • To explore the physiological basis of the slow phase of relaxation and its correlation with electrical activity.

    Main Methods:

    • Contractile responses of chicken embryonic heart cell aggregates were measured using a photodiode.

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  • Photodiode output was correlated with the movement of the aggregate's edge.
  • Experimental maneuvers were used to alter contractile force, and relaxation phases were analyzed.

    • Main Results:

    • Cardiac muscle relaxation exhibits a rapid phase (approx. 100 ms) and a slow phase (over 10 sec).
    • The slow phase of relaxation is independent of viscoelasticity.
    • The rate of relaxation, particularly the slow component, correlates with the rate of depolarization during the pacemaker potential.
    • Reduced automaticity (cooling, spontaneous variation, overdrive pacing) impairs the slow relaxation component.

    Conclusions:

    • The slow phase of cardiac muscle relaxation is physiologically distinct from viscoelasticity.
    • Intracellular calcium removal appears to control diastolic potassium permeability in cardiac aggregates.
    • Both the pacemaker potential slope and the slow relaxation component may reflect the common process of intracellular free calcium removal from the cytoplasm.