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Related Experiment Videos

Axonal surface charges: evidence for phosphate structure.

J S D'Arrigo

    The Journal of Membrane Biology
    |July 24, 1975
    PubMed
    Summary

    Uranyl ions neutralize crayfish axon surface charges, altering alkaline-earth cation effects on spike initiation thresholds. This suggests membrane phospholipids

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    Area of Science:

    • Neuroscience
    • Biophysics
    • Cell Biology

    Background:

    • The threshold membrane potential for nerve impulse initiation is crucial for neuronal function.
    • Extracellular cations influence membrane potential by interacting with surface charges.
    • Uranyl ions (UO2/2+) are known to bind to charged groups on cell surfaces.

    Purpose of the Study:

    • To investigate the effect of extracellular alkaline-earth cations (Ca2+, Mg2+, Sr2+, Ba2+) on crayfish axon spike initiation thresholds.
    • To determine how uranyl ions (UO2/2+) modify the influence of these cations on the threshold potential.
    • To elucidate the nature of surface acidic groups and ion channels involved in action potential generation.

    Main Methods:

    • Intracellular microelectrode recordings were used to measure the threshold membrane potential in crayfish axons.
    • Experiments were conducted at varying extracellular concentrations of uranyl ions (1.0, 3.0, and 9.0 x 10^-6 M).
    • The effects of 50 mM alkaline-earth cations were assessed at each uranyl ion concentration.

    Main Results:

    • Uranyl ions significantly altered the selectivity sequences of alkaline-earth cations affecting the threshold potential, indicating neutralization of surface charges.
    • Observed selectivity sequences varied with uranyl ion concentration, aligning with equilibrium selectivity theory.
    • Uranyl ions did not affect the shape of the action potential itself at the tested concentrations.

    Conclusions:

    • The results suggest that phosphate groups of membrane phospholipids constitute many surface acidic groups near sodium gates.
    • The 'm gates' involved in spike initiation are likely proteinaceous in structure.
    • Uranyl ion interactions provide insights into the surface charge properties and gating mechanisms of neuronal membranes.

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