Inhibition of high K+-induced contraction by the ROCKs inhibitor Y-27632 in vascular smooth muscle: possible involvement of ROCKs in a signal transduction pathway.
In the isolated rat aorta, a ROCKs (rhoA-dependent coiled coil serine/threonine kinases) inhibitor, Y-27632, inhibited the contractions induced not only by receptor agonists but also by high K(+) with the similar IC(50) values (0.8 - 4.9 microM). However, Y-27632 did not inhibit the increment of cytosolic Ca(2+) concentration ([Ca(2+)](i)) due to these stimulants. The Y-27632-induced inhibition of contraction was accompanied by an inhibition of myocin light chain (MLC) phosphorylation, although inhibition of contraction was stronger than that of MLC phosphorylation during the initial phase of contraction. Y-27632 had no effect on the myocin light chain kinase (MLCK) activity. This inhibitor also did not directly change the phosphatase activity. These results suggest that Y-27632 is a selective inhibitor of ROCKs with no direct inhibitory effect on [Ca(2+)](i), calmodulin, MLCK, or phosphatase. Y-27632 disrupted the actin filament network and decreased the filamentous actin, implying that the stronger inhibition by Y-27632 on early phase of contraction than MLC phosphorylation may be explained by this effect. These results suggest that the high K(+)-induced MLC phosphorylation and contraction are mediated not only by the classical Ca(2+)/calmodulin-dependent MLCK system but also by a novel MLC phosphorylation pathway involving ROCKs. One of the possibilities is that high K(+) activates ROCKs to inhibit myosin phosphatase resulting in an augmentation of MLC phosphorylation and contraction.
Sakamoto
Kazuyuki
K
Department of Veterinary Pharmacology, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Japan.
Hori
Masatoshi
M
Izumi
Masanori
M
Oka
Tatsuya
T
Kohama
Kazuhiro
K
Ozaki
Hiroshi
H
Karaki
Hideaki
H
D000199:Actins / Q000378:metabolism; D000577:Amides / Q000494:pharmacology*; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D018994:Myosin Light Chains / Q000378:metabolism; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology*; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction; D013045:Species Specificity; D054460:rho-Associated Kinases
D000199:Actins; D000577:Amides; D047908:Intracellular Signaling Peptides and Proteins; D018994:Myosin Light Chains; D011725:Pyridines; C108830:Y 27632; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D009219:Myosin-Light-Chain Kinase; D043263:Myosin-Light-Chain Phosphatase; D002118:Calcium