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Related Experiment Videos

Contraction bands: differences between physiologically vs. maximally activated single heart muscle cells.

J W Krueger, B London

    Advances in Experimental Medicine and Biology
    |January 1, 1984
    PubMed
    Summary

    High-resolution microscopy revealed distinct differences in rat heart cell striations during contraction. These optical variations suggest myosin head distribution changes, explaining the cardiac length-tension relationship.

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    Area of Science:

    • Cell biology
    • Biophysics
    • Muscle physiology

    Background:

    • Cardiac muscle contraction involves the sliding of myofilaments within sarcomeres.
    • Understanding the structural changes during contraction is crucial for elucidating cardiac function.
    • Previous models assumed fixed myofilament dimensions during shortening.

    Purpose of the Study:

    • To investigate the optical and structural changes in sarcomeres of rat heart cells during shortening.
    • To compare striation patterns in chemically skinned versus electrically stimulated intact cells.
    • To determine if myofilament dimensions are fixed during physiological contraction.

    Main Methods:

    • High-resolution interference and phase microscopy.
    • Chemical skinning of isolated rat heart cells.

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  • Graded shortening induced by calcium addition.
  • Electrical stimulation of intact rat heart cells.
  • Barium contracture for maximal activation.
  • Light diffraction analysis.

    • Main Results:

    • Chemically skinned cells showed contraction densities, I band disappearance, A band phase brightening, and contraction bands consistent with uniform myofilament sliding.
    • Intact cells exhibited distinct A bands without these changes, even at shortened lengths.
    • Light diffraction indicated narrower protein distribution in physiologically shortened sarcomeres.
    • Maximal activation of intact cells induced the same striation changes as in skinned cells.

    Conclusions:

    • Physiological contraction in intact cardiac cells differs optically from chemically induced contraction.
    • The observed optical differences suggest a restricted distribution of myosin heads at sarcomere ends.
    • This restricted myosin head distribution may explain the narrow cardiac length-tension relationship.