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Related Experiment Videos

Calcium binding to intestinal membranes.

J L Oschman, B J Wall

    The Journal of Cell Biology
    |October 1, 1972
    PubMed
    Summary
    This summary is machine-generated.

    Calcium in routine electron microscopy fixatives causes electron-opaque deposits near cell membranes. This artifact, particularly in insect midgut, mimics ion localization techniques and highlights calcium

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    Area of Science:

    • Cell Biology
    • Microscopy Techniques
    • Biochemistry

    Background:

    • Routine electron microscopy fixatives, such as glutaraldehyde and buffer solutions, often contain calcium.
    • Calcium presence in fixatives can lead to the formation of electron-opaque deposits adjacent to cellular membranes.
    • These deposits can be mistaken for specific ion localizations, potentially confounding experimental results.

    Purpose of the Study:

    • To investigate the origin and nature of electron-opaque deposits observed in tissues prepared for electron microscopy.
    • To determine the role of calcium in the formation of these deposits.
    • To clarify the implications of calcium-induced artifacts for ion localization studies.

    Main Methods:

    • Flame photometry was used to quantify calcium levels in glutaraldehyde and buffer solutions.

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  • Various tissues, including insect intestine, were fixed using solutions with and without calcium.
  • Electron microscopy was employed to visualize cellular structures and deposits, with and without post-fixation treatments and varying ion concentrations.

    • Main Results:

    • Calcium was detected in commonly used electron microscopy fixatives.
    • Electron-opaque deposits adjacent to plasma membranes, particularly in insect midgut, correlated directly with the presence of calcium in fixatives.
    • These deposits were observed even with trace amounts of calcium (as low as 5 x 10(-5)M) and could be mimicked by other divalent cations (Mg++, Sr++, Ba++, Mn++, Fe++), but not monovalent ions.
    • Deposits appeared along junctional membranes and, after specific postfixation, resolved to the inner leaflet of apical and lateral plasma membranes, suggesting localization of calcium-binding membrane constituents.

    Conclusions:

    • Calcium contamination in electron microscopy fixatives is a common source of artifactual electron-opaque deposits.
    • These calcium-induced deposits can be misinterpreted as specific ion localizations, impacting studies on ion transport and cell communication.
    • Careful control of calcium levels in fixatives and wash solutions is crucial for accurate ultrastructural and ion localization studies.