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The potassium current underlying delayed rectification in cat ventricular muscle.

T F McDonald, W Trautwein

    The Journal of Physiology
    |January 1, 1978
    PubMed
    Summary
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    This study characterizes outward currents in cat ventricular fibers, identifying fast (I(K)) and slow (I(x)) components. Findings reveal voltage-dependent properties and similarities to other cardiac tissues.

    Area of Science:

    • Electrophysiology
    • Cardiac Physiology
    • Ion Channel Function

    Background:

    • Ventricular myocytes exhibit complex outward currents crucial for action potential repolarization.
    • Understanding these currents is vital for comprehending cardiac electrical activity and arrhythmias.

    Purpose of the Study:

    • To investigate and characterize the time-dependent outward currents in cat ventricular fibers.
    • To differentiate and analyze the properties of fast (I(K)) and slow (I(x)) outward current components.

    Main Methods:

    • Single sucrose gap voltage-clamp technique applied to cat ventricular fibers.
    • Analysis of membrane currents during depolarizing voltage pulses.
    • Manipulation of external potassium (K+) concentrations to assess ionic influences.

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    Main Results:

    • Outward currents resolved into fast I(K) and slow I(x) components with distinct voltage dependencies.
    • I(K) activation threshold around -50 mV, with amplitude increasing steeply between -30 and +10 mV.
    • Current-voltage relations exhibited inward rectification; increased external K+ altered conductance and induced cross-overs.

    Conclusions:

    • I(K) in ventricular muscle shares similarities with i(x1) in Purkinje fibers.
    • Extracellular K+ depletion contributes to time-dependent current variations.
    • Conductance, rather than K+ accumulation, primarily drives the slow outward current I(x).