Rho-associated kinase directly induces smooth muscle contraction through myosin light chain phosphorylation.
Small GTPase Rho plays pivotal roles in the Ca2+ sensitization of smooth muscle. However, the GTP-bound active form of Rho failed to exert Ca2+-sensitizing effects in extensively Triton X-100-permeabilized smooth muscle preparations, due to the loss of the important diffusible cofactor (Gong, M. C., Iizuka, K., Nixon, G. , Browne, J. P., Hall, A., Eccleston, J. F., Sugai, M., Kobayashi, S. , Somlyo, A. V., and Somlyo, A. P. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 1340-1345). Here we demonstrate the contractile effects of Rho-associated kinase (Rho-kinase), recently identified as a putative target of Rho, on the Triton X-100-permeabilized smooth muscle of rabbit portal vein. Introduction of the constitutively active form of Rho-kinase into the cytosol of Triton X-100-permeabilized smooth muscle provoked a contraction and a proportional increase in levels of monophosphorylation of myosin light chain in both the presence and the absence of cytosolic Ca2+. These effects of constitutively active Rho-kinase were wortmannin (a potent myosin light chain kinase inhibitor)-insensitive. Immunoblot analysis revealed that the amount of native Rho-kinase was markedly lower in Triton X-100-permeabilized tissue than in intact tissue. Our results demonstrate that Rho-kinase directly modulates smooth muscle contraction through myosin light chain phosphorylation, independently of the Ca2+-calmodulin-dependent myosin light chain kinase pathway.
Kureishi
Y
Y
First Department of Internal Medicine, Mie University School of Medicine, Tsu, Mie 514, Japan.
Kobayashi
S
S
Amano
M
M
Kimura
K
K
Kanaide
H
H
Nakano
T
T
Kaibuchi
K
K
Ito
M
M
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003902:Detergents / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000378:metabolism*; D018994:Myosin Light Chains / Q000378:metabolism*; D017830:Octoxynol / Q000494:pharmacology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011817:Rabbits; D000077191:Wortmannin; D054460:rho-Associated Kinases
D000730:Androstadienes; D003902:Detergents; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D018994:Myosin Light Chains; D017830:Octoxynol; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D002118:Calcium; D000077191:Wortmannin