Stretch-induced myosin light chain phosphorylation and stretch-release-induced tension development in arterial smooth muscle.

Stretching arteries from resting length to 1.7 times the resting length increased myosin light chain phosphorylation from 40 to 70% in a graded fashion, reaching a plateau at 1.6 times the resting length. When the fully stretched arteries were released, active tension developed without any exogenous stimulating agent. This stretch-release-induced tension approached the same magnitude as that of the control K+-induced tension. Stretch-induced phosphorylation and the subsequent tension development upon release of stretch were prevented by incubating the arteries in physiological salt solutions containing ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) or chlorpromazine. The inhibition produced by EGTA was reversible. Stretch-induced phosphorylation decreased as a function of time, regardless of whether stretch was maintained, or slackened slowly, or released quickly. While tension developed upon release of stretch, light chain phosphorylation simultaneously decreased. As tension reached and maintained its maximal value, phosphorylation continued to decrease. Thus, light chain phosphorylation is necessary for activation of arterial muscle contraction, but it need not be maintained during tension development or maintenance.