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Related Experiment Videos

Axonal surface charges: binding or screening by divalent cations governed by external pH.

J S D'Arrigo

    The Journal of Physiology
    |December 1, 1974
    PubMed
    Summary

    Extracellular alkaline-earth cations affect crayfish nerve cell excitability differently at low pH. Ion binding to surface acidic groups explains these varying effects on spike initiation potential.

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    Area of Science:

    • Neuroscience
    • Biophysics
    • Cell Physiology

    Background:

    • Nerve impulse generation relies on membrane potential.
    • Extracellular cations influence neuronal excitability.
    • Alkaline-earth cations are crucial for cellular functions.

    Purpose of the Study:

    • Investigate the impact of extracellular alkaline-earth cations on nerve cell excitability.
    • Determine how pH affects cation influence on membrane potential.
    • Elucidate the mechanisms of cation interaction with neuronal surfaces.

    Main Methods:

    • Used intracellular microelectrodes to measure membrane potential in crayfish axons.
    • Exposed axons to varying concentrations of calcium, magnesium, strontium, and barium ions.
    • Tested solutions at different pH levels (6.00, 5.35, 5.00, 4.65).

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    Main Results:

    • At pH 6.00, all tested cations had similar effects on threshold potential.
    • At pH 5.35 and lower, cation concentration significantly altered threshold potential.
    • Observed distinct cation selectivity sequences at lower pH values, indicating differential binding.

    Conclusions:

    • Cation selectivity varies with extracellular pH.
    • Equilibrium selectivity theory accurately predicts observed cation sequences.
    • Differences in excitable cells relate to the density of ionized surface acidic groups near sodium gates.