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Calcium-mediated decrease of a voltage-dependent potassium current

D L Alkon, J J Shoukimas, E Heldman

    Biophysical Journal
    |December 1, 1982
    PubMed
    Summary

    Elevated intracellular calcium (Ca++) reduces a specific potassium current (IA) in Hermissenda photoreceptors. This effect is dependent on extracellular calcium, highlighting its crucial role in cellular signaling.

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    Area of Science:

    • Neuroscience
    • Cell Physiology
    • Photoreceptor Biology

    Background:

    • Type B photoreceptors in Hermissenda crassicornis exhibit voltage-dependent potassium currents.
    • Intracellular calcium (Ca++) levels play a role in modulating neuronal function.

    Purpose of the Study:

    • To investigate the effect of elevated intracellular Ca++ on voltage-dependent potassium currents (IA and IB) in Hermissenda photoreceptors.
    • To determine the role of extracellular calcium in mediating these effects.

    Main Methods:

    • Utilized voltage and light-dependent Ca++ currents and direct Ca++ iontophoresis to increase intracellular Ca++.
    • Substituted Barium (Ba++) for Ca++ and removed extracellular Ca++ to assess Ca++ dependency.
    • Measured changes in early (IA) and delayed (IB) potassium currents.

    Main Results:

    • Elevated intracellular Ca++ significantly reduced the amplitude of the early potassium current (IA).
    • This reduction in IA was abolished by removing extracellular Ca++ or substituting Ba++ for Ca++.
    • The delayed potassium current (IB) was also reduced by light and voltage steps, but this was independent of extracellular Ca++.
    • Light alone reduced IB, suggesting a Ca++-independent mechanism.
    • Ca++ iontophoresis abolished the light-dependent Na+ current.

    Conclusions:

    • Intracellular Ca++ concentration is a critical regulator of the early voltage-dependent potassium current (IA) in Hermissenda photoreceptors.
    • Extracellular calcium availability is essential for the Ca++-mediated reduction of IA.
    • A distinct, likely Ca++-independent mechanism underlies the light-induced reduction of the delayed potassium current (IB).

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