Electrophysiological Studies with Gallopamil on the Myocardium of the Human Ventricle
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Anti-arrhythmic substances modify the generation and propagation of impulses in the heart in fundamentally different ways. The distinction between anti-arrhythmic agents with local anaesthetic effects and those with calcium-antagonizing effects is an important one. A local anaesthetic effect means inhibition of the Na+ influx and a calcium-antagonizing effect means inhibition of the influx of Ca2+ during excitation. The currents of Na+ and Ca2+ ions which flow in the myocardial fibres during an action potential are due to the existence of two different systems of ion channels (Reuter 1979). The Na+ channel is essential for the rapid depolarization (phase 0) of the action potential and for the rapid spread of excitation in the atrium and ventricle (fast response). The Ca2+ channel is essential for the plateau (phase 2) of the action potential and the slow depolarization and spread of excitation in the sino-atrial node and AV node (slow response). In the study reported here the effects of gallopamil (methoxy-verapamil, D 600) on action potentials in the isolated human ventricular myocardium were investigated by intracellular recording. These preparations, which are removed as a matter of routine during open heart surgery, can be studied by electrophysiological methods (Trautwein et al. 1962) and are used to assess the direct cardiac effects of drugs in humans.
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