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Related Experiment Videos

Potassium accumulation in smooth muscle and associated ultrastructural changes.

A W Jones, A P Somlyo, A V Somlyo

    The Journal of Physiology
    |July 1, 1973
    PubMed
    Summary

    High potassium solutions increase smooth muscle cell water and alter ultrastructure by reducing extracellular space. However, contractile function remains intact, suggesting resilience to osmotic changes before fixation.

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    Area of Science:

    • Cellular physiology
    • Muscle biology
    • Biophysics

    Background:

    • Understanding smooth muscle cell volume regulation is crucial for interpreting physiological and pathological states.
    • Ionic composition and osmolarity significantly influence cell volume and intracellular structure.

    Purpose of the Study:

    • To investigate the effects of varying ionic compositions and osmolarities on mammalian smooth muscle water content, extracellular space, and ultrastructure.
    • To determine how osmotic changes impact smooth muscle contractility and filament organization.

    Main Methods:

    • Incubation of smooth muscles in solutions with altered ionic concentrations (e.g., high KCl) and osmolarities.
    • Measurement of cell water, extracellular space using (60)CoEDTA, and ionic composition.
    • Ultrastructural analysis via electron microscopy.

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  • Assessment of contractile responses.

    • Main Results:

    • High KCl solutions increased cell water and K+ and Cl- content, reducing extracellular space and causing fiber swelling and nuclear changes.
    • Swelling-induced ultrastructural alterations were prevented by adding sucrose or by depolarization in high K2SO4 solutions.
    • Contractile responses were similar in swollen (high KCl) and unswollen (high K2SO4) muscles, indicating functional filament integrity.
    • Hypertonic shrinkage led to thick filament aggregation, and osmotic shifts during fixation can create artifacts.

    Conclusions:

    • Smooth muscle cell volume regulation is sensitive to extracellular ionic composition and osmolarity.
    • While osmotic stress alters ultrastructure, the contractile apparatus remains functional over a range of separations.
    • Artifacts during fixation can complicate the interpretation of smooth muscle ultrastructure, particularly the filament lattice.