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Effects of quinidine sulfate on the balance among active and passive cellular properties that comprise the electrophysiologic matrix and determine excitability in sheep Purkinje fibers.

Abstract：

:Quinidine is the most commonly used drug for the chronic treatment of ventricular arrhythmias, but it may be arrhythmogenic. Much information exists concerning quinidine's effects on active properties in cardiac tissues, but virtually nothing is known of its effects on passive properties. We studied the effects of quinidine, in a clinically relevant concentration, on the balance among active and passive cellular properties that comprise the electrophysiologic matrix that determines cardiac excitability. The multiple microelectrode method of intracellular-current application and transmembrane voltage recording was used in sheep Purkinje fibers to determine strength-duration and constant current-voltage relations as well as cable properties. A rapid, on-line computerized data analysis system tracked in time the alterations in the active and passive properties relevant to excitability. In normal fibers at [K+]o = 5.4 mM, quinidine increased cardiac excitability as manifested by a decrease in the current required to attain threshold and/or a downward shift in strength- and charge-duration relations by altering passive properties despite a depressed sodium system and a slowed conduction velocity. During washout, excitability and passive properties remained altered despite a return of descriptive action potential parameters such as the resting potential, the maximum rate of rise of phase 0, overshoot, and the action potential duration to or nearly to normal. At [K+]o = 8.0 mM, quinidine could either increase or decrease excitability; net excitability depends on the balance between altered passive properties and the depressed sodium system. The results explain, in part, the antiarrhythmic actions and arrhythmogenic potential of quinidine. The data for quinidine and other antiarrhythmic drugs are interpreted in terms of the electrophysiologic matrix, which we believe has important advantages over traditional hierarchical classifications.

journal_name

Circ Res

journal_title

Circulation research

authors

Arnsdorf MF,Sawicki GJ

doi

10.1161/01.res.61.2.244

subject

Has Abstract

pub_date

1987-08-01 00:00:00

pages

244-55

issue

eissn

0009-7330

issn

1524-4571

journal_volume

pub_type

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Effects of quinidine sulfate on the balance among active and passive cellular properties that comprise the electrophysiologic matrix and determine excitability in sheep Purkinje fibers.