Ischaemia-induced changes in the phosphorylase activity in different parts of the cardiac conduction system

The phosphorylase specific activity was lowered in total ischaemia in all examined parts of the myocardium and the conduction system of the heart. Sixty-minute ischaemia had a considerable effect on glycogen degradation in right bundle branch and in the working myocardium, however, its glycogenolytic effect on the AV-node and penetrating bundle of His was insignificant. Phosphorylase "a" evaluated as a percentage of the total phosphorylase activity decreased in the working myocardium and increased in the AV-node during ischaemia. The data obtained support the hypothesis according to which conductive tissue is more resistant to ischaemia than the working myocardium. The results serve evidence that the right bundle branch is more susceptible to metabolic damage caused by ischaemia than the AV-node and penetrating bundle of His.