Contraction in intact pig aortic strips is not always associated with phosphorylation of myosin light chains

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Abstract
Intact pig aortic strips were incubated in medium containing [32P]Pi and various Ca2+ concentrations. The 32P content of the myosin P-light chain was determined by radioautography after electrophoresis in the presence of sodium dodecyl sulfate. Although treatment of the strips with noradrenaline [norepinephrine] always caused a rise in tension, this was not necessarily accompanied by increased phosphorylation of the P-light chain. In aortic smooth muscle, phosphorylation of the P-light chain apparently is not obligatory for contraction.