Phosphorylation-dependent activated tension in skinned gizzard muscle fibers in the absence of Ca2+.
A Ca2+-insensitive myosin light chain kinase was prepared and used in experiments with skinned gizzard fibers. In the absence of Ca2+, this kinase activated isometric force development. The force development was associated with phosphorylation of the 20,000-dalton myosin light chains and addition of Ca2+ did not activate the fibers further. Pretreatment of the fibers with Ca2+-insensitive myosin light chain kinase and adenosine 5'-O-(3-thiotriphosphate) in the absence of Ca2+ caused thiophosphorylation of the light chains and, on the addition of ATP, an activation of isometric tension was observed. The subsequent addition of Ca2+ did not increase force development. A comparison of Ca2+-activated tension in the skinned gizzard muscle fibers with Ca2+-insensitive myosin light chain kinase-activated tension suggests that the phosphorylation of the myosin light chains is the dominant factor in the development of tension in smooth muscle.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002645:Chickens; D005895:Gizzard, Avian / Q000201:enzymology; D007700:Kinetics; D008970:Molecular Weight; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000201:enzymology*; D009219:Myosin-Light-Chain Kinase; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*
D011494:Protein Kinases; D009219:Myosin-Light-Chain Kinase; D002118:Calcium