Abstract
1. Electrical and mechanical responses to catecholamines were studied in isolated ring muscle strips of the coronary artery of the dog.
2. Adrenaline and noradrenaline caused various responses of large coronary artery and relaxation of the small coronary artery. Isoprenaline caused relaxation of both large and small coronary artery.
3. Catecholamine-induced relaxation or contraction was blocked by beta or alpha adrenergic blockade respectively.
4. The mean, resting membrane potential of small coronary artery recorded intracellularly was -47 mV.
5. Adrenaline caused relaxation without changes in the membrane potential and in the absence of action potentials.
6. Increase in extracellular potassium initiated depolarization of cell membrane.
7. Dissociation in smooth muscle between relaxation and membrane potential change were discussed.
