Phosphorylation of the 20,000-dalton light chain of myosin of intact arterial smooth muscle in rest and in contraction.

The 20,000-dalton myosin light chain of intact pig carotid arteries was found to be rapidly labeled when the arterial muscle was incubated in physiological salt solution at 37 degrees C containing [32P]orthophosphate. Light chain phosphorylation in the intact muscle had a marked requirement for Ca2+ and was dependent upon the passive tension applied to the muscle. Norepinephrine- or KCl-induced contractures were associated with concomitant increases in light chain phosphorylation.