4-Aminopyridine and the early outward current of sheep cardiac Purkinje fibers.
Open Access
- 1 February 1979
- journal article
- research article
- Published by Rockefeller University Press in The Journal of general physiology
- Vol. 73 (2), 139-157
- https://doi.org/10.1085/jgp.73.2.139
Abstract
The effects of the K-blocking agent 4-aminopyridine (4-AP) on the action potential and membrane currents of the sheep cardiac Purkinje fiber were studied. 4-AP slowed the rate of phase 1 repolarization and shifted the plateau of the action potential to less negative potentials. In 4-AP, the substitution of Na methylsulfate or methanesulfonate for the NaCl or Tyrode''s solution further slowed the rate of phase 1 repolarization, even though Cl replacement has no effect on the untreated preparation. In voltage clamp experiments. 4-AP rapidly and reversibly reduced the early peak of outward current that occurs when the Purkinje fiber membrane is voltage-clamped to potentials positive to -20 mV. In addition, 4-AP reduced the steady outward current at the end of clamp steps positive to -40 mV. 4-AP did not change the slow inward current over the range of -60 to -40 mV, nor did it greatly change the current tails that were used as a measure of slow inward conductance at more positive potentials. 4-AP did not block the inward rectifying K currents, IK1 and IK2. A phasic outward current component that was insensitive to 4-AP was reduced by Cl replacement. The early outward current has 2 components: a Cl-sensitive component plus a 4-AP-sensitive component. Since a portion of the steady-state current was sensitive to 4-AP, the early outward current does not fully inactivate or 4-AP blocks a component of time-independent background current.This publication has 30 references indexed in Scilit:
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