Electrophysiological studies of the interaction between ventricular myocardium and coronary artery in monkeys.

1. The electrical influence of the coronary arteries on ventricular muscle was investigated using strips of ventricle that included a section of coronary artery (cardiac preparation) and isolated coronary arteries dissected from the ventricle (arterial preparation). 2. In cardiac preparations, a hyperpolarizing response was recorded from the epicardial surface of the ventricular muscle when acetylcholine (ACh) was added to the organ bath, on condition that the internal diameter of the coronary artery was between 0.15 and 0.6 mm, that the vessel ran at a depth of 0.2 mm or less below the surface of the preparation, and that the recording microelectrode was immediately adjacent to the artery. 3. ACh-induced hyperpolarization was not detected in cardiac preparations which had no detectable arteries, or at sites distant from visible arteries. 4. In arterial preparations, a similar hyperpolarizing response was evoked by ACh in all vessels with an i.d. of 0.15-1.2 mm. 5. In a preparation combining ventricular muscle and a strip of coronary artery (with the vascular endothelium in direct contact with the epicardial surface of the ventricular myocardium), hyperpolarization was also observed from the ventricular muscle after application of ACh. 6. The hyperpolarizing response of the ventricular myocardium in the cardiac preparation and in combined preparations of ventricular muscle and coronary artery was weakened or abolished by removal of the arterial endothelium. 7. These results indicate that some substance released from the coronary arterial endothelium after stimulation by ACh induces hyperpolarization of the ventricular myocardium.