Effects of cyclopropane and of hypoxia on transmembrane potentials of atrial, ventricular and Purkinje fibers.

• The action of cyclopropane in sensitizing the myocardium to catecholamines has been the subject of numerous investigations."" Little information is available on the effects of cyclopropane alone on cellular processes in cardiac tissue. Recently, however, using electrophysiological recording techniques, Smith et al. found that the ventricular strengthinterval curve shifted to the right in dogs anesthetized with cyclopropane. This was interpreted as indicating a decrease in ventricular excitability. Levy et al. studied the effects of cyclopropane on transmembrane potentials of rabbit atrium and ventricular fibers of dogs anesthetized with cyclopropane. The action potential was shortened in duration in the former tissue while no changes could be detected in in situ ventricular muscle fibers. Recent studies of Moore et al. suggest that the ventricular arrhythmias elicited by catecholamines in dogs treated with cyclopropane arise in the ventricular conducting system. It is possible that cyclopropane exerts on cardiac tissues some direct effect which is in part responsible for the development of arrhythmias. The present paper reports the effects of cyclopropane and of hypoxia on transmembrane potentials of single Purkinje, ventricular, and atrial muscle fibers.