Cyclic adenosine 3', 5'-monophosphate, adenyl cyclase and phosphodiesterase in the conduction system of bovine heart.

Cyclic adenosine 3', 5'-monophosphate (cyclic AMP) and adenyl cyclase and phosphodiesterase activities were determined in the specialized myocardial tissue of the conduction system of bovine heart and then compared with those in the ordinary myocardial tissue. The conduction system was comprised of the atrioventricular node (A-V node), the His bundle and the right and the left bundle branches (RBB and LBB). The content of cyclic AMP was higher in the ordinary myocardial tissue than in the specialized myocardial tissue. In the specialized myocardial tissue, its content was highest in the A-V node and lower in the His bundle than in the LBB and the difference between the contents in the RBB and the LBB was not significant. Adenyl cyclase activity as well as the content of cyclic AMP was higher in the ordinary myocardial tissue than in the specialized myocardial tissue. Its activity was higher in the A-V node than in the His bundle or the RBB, and the activities in the His bundle, the RBB and the LBB were similar. Phosphodiesterase activity was higher in the ordinary myocardial tissue than in the A-V node, and the activities in these 4 sections of the conduction system were similar.