Electrical responses of coronary artery smooth muscle associated with the cardiac muscle action potential in the monkey.

1. In cardiac strips of the monkey ventricle which included a section of coronary artery (cardiac preparation), a depolarizing response, which appeared to be an excitatory junction potential (EJP), and a hyperpolarizing response were observed from the coronary artery smooth muscles when an action potential was generated in cardiac muscle by the application of electrical stimulation to the cardiac muscle alone. 2. In an isolated preparation of the coronary artery dissected from the ventricle (arterial preparation), similar responses, an EJP and a hyperpolarizing response, could be evoked by electrical stimulation. 3. In the cardiac preparation, the threshold of electrical stimulation for generation of the cardiac action potential and for production of an electrical response in the vascular smooth muscle were the same. 4. The EJP and the hyperpolarizing responses of the smooth muscle of the coronary artery ceased or were weakened by elimination of the adventitial connective tissues and endothelium, respectively, in both the cardiac preparation and the coronary artery preparation. 5. These results indicate that the action potential of cardiac muscle generated by electrical stimulation activates the nerves and the vascular endothelium, which, in turn, produce an EJP and a hyperpolarizing response of the coronary artery smooth muscle, respectively.