Adenylate cyclase activity in various components of the sarcoplasmic reticulum: a cytochemical study of ventricular biopsies from diseased human hearts.

Localization of adenylate cyclase (ACLase) activity was studied in biopsies of diseased human myocardium by means of electron microscopic cytochemistry. Five right and seven left ventricular biopsy specimens were obtained from patients with idiopathic dilated (3 cases) and hypertrophic (3 cases) cardiomyopathies, various acquired (3 cases) and congenital (1 case) heart diseases, and other heart diseases (2 cases). Catecholamine-stimulated ACLase activity was assessed relative to the fine structure of cardiocytes. The most intense ACLase activity was found in the sarcoplasmic reticulum (SR), but activity was also present in the sarcolemma. The enzyme activity was present in a wide morphologic spectrum of components of the SR, including junctional SR of internal and peripheral coupling (12 cases), free SR in association with myofibrils (6 cases), and free SR in association with mitochondria (5 cases). ACLase activity in junctional SR in the human myocardium resembles the findings in hearts of other mammalian species. The enzyme activity in human myocardial SR may represent a local regulatory function of the ACLase-cyclic AMP-phosphodiestrerase system in the SR components.