Electrophysiological properties of the smooth muscle cell membrane of the dog coronary artery.

1. The electrical properties of dog coronary arterial smooth muscles were studied with the partitioned chamber method and Wheatstone Bridge method. Effects of intracellular and extracellular current and of field stimulation of nerve were examined. 2. Muscle from the anterior descending coronary artery showed cable properties, with a 2.4 mm space constant and a 455 msec time constant. Muscle strips from the circumflex coronary artery showed poor cell-to-cell connexions. 3. The smooth muscle of both coronary arteries was electrically quiescent and action potentials were not evoked even by strong outward current. 4. Field stimulation of the descending coronary artery induced either contraction or relaxation which were respectively associated with depolarization and hyperpolarization. These responses were blocked by tetrodotoxin (2 x 10(-7) g/ml). 5. Field stimulation produced depolarization when the membrane potential was higher than 60 mV and hyperpolarization when the membrane potential was lower than -50 mV. 6. The results suggest that, in the descending coronary artery, the smooth muscle including the innermost cells can be controlled by nerve.