[Antiarrhythmic effects of magnesium on single ventricular myocytes]

Despite magnesium ions (Mg)'s widespread use for antiarrhythmic purposes, little is known concerning its antiarrhythmic mechanisms. We, therefore, examined Mg effects on delayed afterdepolarization (DAD), early afterdepolarization (EAD), triggered activity (TA) and aftercontraction (AC), using isolated ventricular cells and/or ventricular papillary muscle. In the experiments using the multicellular preparation, ACs were measured, with the use of a strain gauge. ACs were induced in isolated rat papillary muscle superfused with low K+ (0.5 mM) medium, after a train stimulation (2-5 Hz, 10-30 beats). In the experiments concerning cardiac myocytes, the effects of Mg on transient inward current (TI), which is responsible for DAD, were studied using a whole-cell voltage-clamp method applied on isolated guinea pig ventricular cells. And action potentials were also induced by current clamp (10 ms) and the effects of Mg on DAD, EAD and TA were examined. TI, DAD, EAD and TA were induced by use of pipette solution with high Ca2+ (0.7 mM) and low EGTA (0.1 mM).(ABSTRACT TRUNCATED AT 250 WORDS)