Effects of Calcium and Cylopropane on Purkinje Fibers

Abstract

Purkinje fibers isolated from the dog heart were perfused with Tyrode solution containing cyclopropane (6 to 8 vol.%) and normal calcium concentration (2.7 mmoles/liter). Transmembrane action potentials recorded during perfusion were compared with those obtained during subsequent perfusion with cyclopropane in solution containing 0.675(¼×), 1.35(½×), 5.4(2×) or 10.8(4×) mmoles/liter of CaCl2. In either of the low calcium solutions, the acceleration of repolarization during the plateau of the action potential initiated by cyclopropane was reversed, with the result that the contour of the action potential returned to that present prior to treatment with cyclopropane. Continued treatment with ¼× solution caused a general deterioration of the action potential. In both 2× and 4× solutions, the action of cyclopropane on repolarization was enhanced, that is repolarization occurred more rapidly. In addition the latter procedure increased the rate and magnitude of diastolic depolarization. The possible effects of these changes in configuration of action potential on ventricular excitability and on the tendency for the development of arrhythmias during cyclopropane anesthesia are discussed.