Temperature modulates calcium homeostasis and ventricular arrhythmias in myocardial preparations

Objective: The aim was to evaluate the effect of temperature on reoxygenation induced ventricular arrhythmias in isolated hearts, on delayed afterdepolarisations and Iti current in Purkinje fibres, and on sarcoplasmic reticular function and Ca2+ handling of single cardiac myocytes. Methods: Isolated guinea pig hearts were retrogradely perfused at 37°C with a hypoxic medium for 15 min and reoxygenated for 10 min either at 33°C or at 37°C. Intracellular microelectrodes were used to assess the presence of delayed afterdepolarisations and triggered activity in sheep Purkinje fibres exposed to strophanthidin at different temperatures. Iti current was evaluated in voltage clamp experiments. In rat cardiomyocytes, loaded with the fluorescent Ca2+ dye, indo-1, the sarcoplasmic reticular Ca2+ content was assessed at 30°C and at 37°C, either by a caffeine spritz puffed onto a cell from a patch pipette or by a post-rest contraction. Results: Hypothermic reoxygenation reduced the incidence of ventricular arrhythmias in isolated hearts (30%, n = 10, at 33°C and 75%, n = 30, at 37°C, p < 0.05). In Purkinje fibres, hypothermia decreased the amplitude of delayed afterdepolarisations. Moreover, at 32°C, the amplitude of Iti current was decreased to 59.2(SEM 2.6)% of the normothermic value [27.5(6.7) nA, n = 4, p< 0.005] and time to peak increased to 159.7(10.2)% [value at 37°C = 470(41) ms, n = 4, p