G-PROTEIN-MEDIATED INHIBITION OF MYOSIN LIGHT-CHAIN PHOSPHATASE IN VASCULAR SMOOTH-MUSCLE
G-PROTEIN-MEDIATED INHIBITION OF MYOSIN LIGHT-CHAIN PHOSPHATASE IN VASCULAR SMOOTH-MUSCLE
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DOI：
10.1073/pnas.88.20.9307
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发表时间：
1991-10-01
影响因子：
11.1
通讯作者：
SOMLYO, AP
中科院分区：
文献类型：
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作者：
KITAZAWA, T;MASUO, M;SOMLYO, AP
在受体偶联的α-毒素通透性兔门静脉平滑肌上，研究了G蛋白介导的血管收缩机构对钙离子的增敏机制。为了验证钙敏化是由于抑制肌球蛋白轻链磷酸酶活性的假设，我们测量了5‘-[γ-硫代]三磷酸鸟苷和苯肾上腺素对经钙离子预激活的肌肉肌球蛋白轻链磷酸酶去磷酸化速率的影响，并在含有1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1，4-diazepine(ML-9)的无钙和三磷酸腺苷溶液中孵育以阻断肌球蛋白轻链磷酸酶活性。鸟苷5‘-[γ-硫代]三磷酸(300-mU-M)或与苯肾上腺素合用(3-mU-M)使MLC的松弛和去磷酸化速率降低到对照的一半左右；这种抑制足以解释G蛋白介导的最大的钙敏化MLC的磷酸化。鸟苷5‘-[γ-硫代]三磷酸不影响MLC与腺苷5’-[γ-硫代]三磷酸的硫代磷酸化速率。我们认为，G蛋白(S)对蛋白磷酸酶(S)的抑制可能具有重要的调节作用。
The mechanism of G protein-mediated sensitization of the contractile apparatus of smooth muscle to Ca2+ was studied in receptor-coupled alpha-toxin-permeabilized rabbit portal vein smooth muscle. To test the hypothesis that Ca2+ sensitization is due to inhibition of myosin light-chain (MLC) phosphatase activity, we measured the effect of guanosine 5'-[gamma-thio]triphosphate and phenylephrine on the rate of MLC dephosphorylation in muscles preactivated with Ca2+ and incubated in Ca2+- and ATP-free solution containing 1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine (ML-9) to block MLC kinase activity. Guanosine 5'-[gamma-thio]triphosphate alone (300-mu-M) or in combination (3-mu-M) with phenylephrine decreased the rates of relaxation and dephosphorylation of MLC to about half of control values; this inhibition is sufficient to account for maximal G protein-mediated Ca2+ sensitization of MLC phosphorylation. The rate of thiophosphorylation of MLC with adenosine 5'-[gamma-thio]triphosphate was not affected by guanosine 5'-[gamma-thio]triphosphate. We suggest that inhibition of protein phosphatase(s) by G protein(s) may have important regulatory functions.