In order to relate the cardiac antiarrhytmic properties of magnesium chloride (MgCl2) to its electrophysiological effects, a comparison of its actions on three different models of automaticity of the isolated Purkinje fibers of the dog, has been carried out. The spontaneous activity of the Purkinje fibers perfused with Tyrode's solution containing 2.7 mM KC1 was gradually reduced as MgC12 concentration was increased from 3 to 9 mM/1. The automaticity induced adding barium chloride (BaC12) to the perfusion solution was suppressed increasing the concentration of MgC12 in the Tyrode's solution up to 5 mM/1. Previous increases in the concentration of MgCl2 prevents the electrophysiological effects BaC12. The negative chronotropic effects of MgC12, were less evident on the adrenalin induced automaticity of the Purkinje fibers. Simultaneous addition of adrenalin and MgC12 to the perfusion media increases membrane resting potential action potential amplitude and maximun rate of depolarisation of phase O in Purkinje fibers. It is concluded that MgC12 acts by distinct electrophysiological mechanisms against the different models of cardiac automaticity studied. This findings may provide interesting perspective in respect to the therapeutic properties of magnesium chloride.
Animals Anti-Arrhythmia Agents