Hydrogen peroxide induced changes in membrane potentials in guinea pig ventricular muscle: permissive role of iron

Abstract

Study objective – It has been proposed that oxygen free radicals trigger reperfusion arrhythmias. The mechanism of these arrhythmias is not clear. Thus, the effect of H₂O₂ on cellular action potentials was examined. Design – Trabecular muscles were superfused either with H₂O₂ alone or with H₂O₂ in combination with iron ions or an iron chelating agent or various scavengers of oxygen free radicals. The effect of reduction of the superfusate calcium from 1.8 to 0.2 mmol·litre⁻¹ on H₂O₂ induced changes was also studied. Experimental material – Thin trabecular muscles isolated from the hearts of guinea pigs (200-300 g) of either sex were used. Measurements and main results – H₂O₂ (0.6 mmol·litre⁻¹) caused a reproducible sequence of changes consisting of an initial increase in plateau height and in action potential duration, followed after 12-14 min by rapid action potential shortening accompanied by resting membrane depolarisation, reduction in action potential amplitude and dV/dt_max, and by occasional appearance of late afterdepolarisations, leading finally to loss of excitability. This sequence of changes was: (1) accelerated by higher concentrations of H₂O₂, FeCl₃ (0.1 mmol·litre⁻¹), and FeCl₂ (0.1 mmol·litre⁻¹); (2) prevented by dimethylthiourea (10 mmol·litre⁻¹) and desferrioxamine (2 mmol·litre⁻¹); (3) not influenced by superoxide dismutase (150 units·ml⁻¹), mannitol (5-50 mmol·litre⁻¹) or PBN (50 μmol·litre⁻¹); and (4) not prevented by a reduction of the superfusate calcium. Conclusions – The electrophysiological alterations induced by H₂O₂ are caused by a hydroxyl radical formed intracellularly in the iron catalysed Fenton reaction.