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Effects of 4-aminopyridine on inward rectifying and pacemaker currents of cardiac purkinje fibres

  • Excitable Tissues and Central Nervous Physiology
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Abstract

  1. 1.

    4-Aminopyridine (4-AP), in a concentration of 1–5mM, prolongs the action potential duration, induces spontaneous activity and depolarizes sheep cardiac Purkinje strands. These effects are different from those obtained with 0.1mM and are reversible.

  2. 2.

    Voltage clamp experiments demonstrate that the higher drug concentrations affect membrane currents measured in the potential range between-100 and-40mV, in addition to the reduction of the transient outward current already described for small amounts of the drug (0.1–0.5mM).

  3. 3.

    The analysis of membrane current modifications by 4-AP in the presence of cesium and barium ions indicates that 4-AP, in the higher concentration range, reduces the inward rectifying time independent potassium currenti K1 and modifies the voltage dependence of the time and voltage dependent pacemaker current. The steady-state activation curve of the pacemaker, current is shifted towards less negative potentials and is less steeply voltage dependent. The time constant (τ) curve has an increased maximum, displaced towards less negative potentials.

  4. 4.

    The modifications by 4-AP of thei K1 and pacemaker currents explain the changes in resting potential, action potential duration and the induction of spontaneous activity. The latter effect is not the result of an indirect effect of 4-AP through increased release of neurotransmitters from sympathetic nerve endings. A possible action of 4-AP at the inside of the membrane, explaining the multiple actions, is discussed.

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  1. Laboratory of Physiology, University of Antwerp, (RUCA), Groenenborgerlaan 171, B-2020, Antwerpen, Belgium

    P. P. Van Bogaert & D. J. Snyders

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  1. P. P. Van Bogaert
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  2. D. J. Snyders
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Van Bogaert, P.P., Snyders, D.J. Effects of 4-aminopyridine on inward rectifying and pacemaker currents of cardiac purkinje fibres. Pflugers Arch. 394, 230–238 (1982). https://doi.org/10.1007/BF00589097

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  • DOI: https://doi.org/10.1007/BF00589097

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