Myosin light chain phosphatase activities and the effects of phosphatase inhibitors in tonic and phasic smooth muscle.
Myosin light chain phosphatase activities and the effects of phosphatase inhibitors in tonic and phasic smooth muscle.
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DOI：
10.1016/s0021-9258(18)42092-3
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发表时间：
1992-07
期刊：
影响因子：
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通讯作者：
M. Gong;P. Cohen;Toshio Kitazawa;M. Ikebe;M. Masuo;A. Somlyo;A. Somlyo
中科院分区：
文献类型：
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作者：
M. Gong;P. Cohen;Toshio Kitazawa;M. Ikebe;M. Masuo;A. Somlyo;A. Somlyo
磷酸酶抑制剂微囊藻毒素-LR、互变霉素和冈田酸在β-七叶皂苷透化的阶段性和紧张性平滑肌的无钙溶液中引起收缩并增加20 kDa肌球蛋白轻链（MLC 20）磷酸化，并以相同的效力顺序抑制平滑肌匀浆的重肌球蛋白（HMM）磷酸酶活性：微囊藻毒素-LR大于互变霉素大于冈田酸。对所有三种抑制剂的敏感性显著更高，松弛和去磷酸化的半衰期长4-6倍，并且在强直性股动脉中HMM磷酸酶和MLC 20激酶活性/平滑肌细胞湿重比在阶段性回肠或门静脉平滑肌中低2.0和1.9倍。用0.2 μ M抑制剂-2预孵育可使回肠中的HMM磷酸酶活性降低35%，使股动脉中的HMM磷酸酶活性降低60%。结果表明，平滑肌的HMM磷酸酶具有与1型蛋白磷酸酶相同的特性，但仅部分被高浓度的抑制剂-2抑制，并且强直性平滑肌的较低HMM磷酸酶活性可能有助于其对磷酸酶抑制剂的更大敏感性和其较慢的松弛速率。
Phosphatase inhibitors microcystin-LR, tautomycin, and okadaic acid caused contraction and increased 20-kDa myosin light chain (MLC20) phosphorylation in Ca(2+)-free solutions in both phasic and tonic smooth muscle permeabilized with beta-escin, and inhibited the heavy meromyosin (HMM) phosphatase activity of smooth muscle homogenates with the same potency sequence: microcystin-LR greater than tautomycin greater than okadaic acid. The sensitivity to all three inhibitors was significantly higher, the half-times of relaxation and dephosphorylation were 4-6 times longer, and the HMM phosphatase and MLC20 kinase activity/smooth muscle cell wet weight was 2.0- and 1.9-fold lower in the tonic, femoral artery, than in the phasic, ileum or portal vein, smooth muscle. Preincubation with 0.2 microM inhibitor-2 decreased the HMM phosphatase activity by 35% in the ileum and by 60% in the femoral artery. The results suggest that the HMM phosphatases of smooth muscle have properties common to type 1 protein phosphatases, but are inhibited only partially by high concentrations of inhibitor-2, and that the lower HMM phosphatase activity of tonic smooth muscle may contribute to its greater sensitivity to phosphatase inhibitors and its slower rate of relaxation.