On the antiarrhythmic mechanisms of magnesium in cardiac Purkinje fibers.
The antiarrhythmic actions of high [Mg]o (8 mM) were studied in sheep cardiac Purkinje fibers. At 0.1 microM, strophanthidin inhibits the Na-K pump (intracellular sodium activity aiNa and force increase) and increasing Mg shortens the action potential, decreases force and increases aiNa, as in control. At 1 microM, strophanthidin increases aiNa and force, induces oscillatory potentials (Vos) and arrhythmias: increasing Mg reduces Vos and abolishes arrhythmias but increases aiNa further. High Mg also slows or stops spontaneous activity induced by norepinephrine by a positive shift of the threshold, and decreases Vos in high [Ca]o. Thus, antiarrhythmic mechanisms of high [Mg]o include a shift in threshold potential and a decrease in Vos but not a removal of Na pump inhibition.
Aceto
E
E
Department of Physiology, State University of New York, Brooklyn.
Vassalle
M
M
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D010507:Periodicity; D011690:Purkinje Fibers / Q000187:drug effects*; D012756:Sheep; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects; D013327:Strophanthidin / Q000494:pharmacology
D000889:Anti-Arrhythmia Agents; D013327:Strophanthidin; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D002118:Calcium; D009638:Norepinephrine