Rapid myosin phosphorylation transients in phasic contractions in chicken gizzard smooth muscle.

In intact smooth muscle strips from chicken gizzard, electrical stimulation and carbachol elicited brief, phasic contractions which were associated with a very rapid, transient phosphorylation of the 20 kDa myosin light chains. The phosphorylation transients reached their peak after 3 s and 6 s and preceded that of force. Phosphorylation was not significantly different from basal levels after 10 s and 30 s while force still amounted to 50% of the peak value. The rate of tension decline could be increased by cessation of stimulation or by addition of atropine, even at apparently basal phosphorylation levels suggesting a phosphorylation independent regulation.