The differential response of normal and ischaemic Purkinje fibres to clofilium, d-sotalol and bretylium.

To determine whether ischaemic tissue is more sensitive than normal tissue to class III anti-arrhythmic agents, we studied the effects of the class III agents clofilium, d-sotalol and bretylium on normal and ischaemic Purkinje fibres one day after ligation of canine left anterior descending coronary artery. In ischaemic Purkinje fibres superfused with normal Tyrode's solution (4mM K+, 2.7mM Ca+2) clofilium produced early afterdepolarisations at 10(-7)M and 10(-6)M, d-sotalol at 10(-5)M to 10(-3)M, and bretylium at 10(-3)M. The early afterdepolarisation response of ischaemic tissue, which in some cases prolonged action potential duration to beyond 10 s, was significantly different from the simple prolongation of action potential duration seen in normal Purkinje fibres at the same concentrations. Clofilium and d-sotalol differentially produced early afterdepolarisations at or very near "anti-arrhythmic" doses. Therefore, class III anti-arrhythmics produced early afterdepolarisations differentially in ischaemic tissue at concentrations which did not produce early afterdepolarisations in normal tissue.