Calcium, nifedipine and arrhythmias in isolated rat atria

Arrhythmias were induced in isolated rat atrial muscle preparations by increasing the calcium concentration of the Ringer solution, while the potassium concentration was kept low. A rise in the resting tension occurred simultaneously. The release of aspartate aminotransferase (ASAT) from the fibrillating atria was not higher than the release from non-fibrillating atria pretreated with a calcium-antagonistic drug, nifedipine 100 microgram/l. It is suggested that calcium-induced rat atrial arrhythmias in the present experiments are caused by a direct effect on calcium influx through the excitable membrane and not as a result of myocardial lesion caused by calcium overload.