Calponin phosphorylation does not accompany contraction of various smooth muscles

Calponin phosphorylation was quantitated in 32P-labeled porcine arterial, uterine, tracheal, stomach and bladder smooth muscles. The negligible amount of 0.003-0.008 mol [32P]phosphate/mol calponin in resting muscles did not increase upon contraction induced by various agents, under conditions when myosin light-chain phosphorylation increased several-fold. The results indicate no involvement of calponin phosphorylation is smooth-muscle contraction.