Abstract
Summary and conclusions
Ventricular strips from turtles and frogs were isolated, suspended in air, superfused with buffered Ringer's solution and driven at a constant frequency. The conduction velocity, stimulus threshold, Q-T interval (refractory period), and force of isometric contraction were measured. 1. Ouabain and procainamide elicited their previously documented effects on these isolated ventricular strips. 2. Contrary to a previous report, epinephrine increased the force of contraction of an electrically driven strip of turtle ventricle, but did not affect the other parameters. 3. 5-HT did not alter significantly conduction time, stimulus threshold, Q-T interval or force of contraction of either ventricular strips or of turtle hearts in situ, when applied in neutral, acid, or alkaline solutions. 4. Epinephrine and 5-HT occasionally produced premature systoles and periods of autorhythmicity.
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