Adrenergic stimulation of depolarized arterial muscle.

• Electrical depolarization of the muscle cell membrane lias been generally considered to be an essential part of the physiological excitation of muscle cells which initiates contraction." However, there is direct evidence for electrical inexcitability of the membrane receptors in frog skeletal muscle, and complete depolarization by immersion in isosmotic potassium-rich solution does not abolish the contractile responses of visceral smooth muscle to acetyleholine. Further examination of the question of whether depolarization is an essential step in muscular excitation is therefore indicated.