THE RELATIONSHIP OF INTRACELLULAR DEPOLARIZATION RATES AND CONTRACTILITY IN THE DOG VENTRICLE IN SITU: EFFECTS OF POSITIVE AND NEGATIVE INOTROPIC AGENTS

¹ Department of Pharmacology, Medical College of South Caroline, Charleston, South Carolina

The proposal by previous investigators that the influx of sodium during the depolarization phase of cardiac action potentials released bound calcium from the sarcoplasmic reticulum, which in turn initiated contraction, suggested to us that a relationship should exist between the depolarization phase of the action potential and contraction. This relationship has been investigated through a study of the effects of positive and negative inotropic agents on the two parameters. A new technique was used to record transmembrane potentials from ventricular muscle of dogs with intact circulation. The various parameters were recorded on magnetic tape and recalled in a time-expanded mode to facilitate critical analyses. Digoxin produced concomitant increments in maximal rate of depolarization of action potentials and in contractile force, and quinidine and cocaine correspondingly decreased both these parameters. A statistically significant relationship was shown to exist between the maximal rate of depolarization and contractile force.

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