van Riper D A, McDaniel N L, Rembold C M
Department of Internal Medicine, University of Virginia Health Science Center, Charlottesvile 22908, USA.
Biochim Biophys Acta. 1997 Mar 1;1355(3):323-30. doi: 10.1016/s0167-4889(96)00144-9.
Nitrovasodilators are hypothesized to induce smooth muscle relaxation by their metabolism to nitric oxide, which then activates soluble guanylyl cyclase, increases [cGMP], and activates cGMP-dependent protein kinase. cGMP-dependent phosphorylation is then proposed to decrease intracellular [Ca2+] ([Ca2+]i) and to reduce the Ca(2+)-sensitivity of contraction. We hypothesized that one component of decreased Ca(2+)-sensitivity, reduced Ca(2+)-sensitivity of MLC phosphorylation, was due to phosphorylation of myosin light chain kinase (MLCK) on the peptide site A. In the swine carotid artery, histamine (10 microM) stimulation increased aequorin-estimated [Ca2+]i, MLCK site A phosphorylation, MLC phosphorylation, and force. Subsequent addition of 100 microM nitroglycerin (NTG) or 100 microM sodium nitroprusside (NP) to histamine-stimulated tissues increased [cGMP], decreased both MLC phosphorylation and force, but did not significantly alter [cAMP], [Ca2+]i, or MLCK site A phosphorylation. Addition of NTG and NP alone to unstimulated tissues increased MLCK site A phosphorylation, but did not alter [Ca2+]i. In tissues preincubated with NP, subsequent histamine contraction was slowed compared with controls, however, this slowed rate of contraction appeared to result from an attenuation of histamine-dependent increases in [Ca2+]i. These data suggest that, in swine carotid artery, nitrovasodilators can decrease the Ca(2+)-sensitivity of MLC phosphorylation without increasing MLCK site A phosphorylation. Nitrovasodilators, per se, can induce site A MLCK phosphorylation, potentially by cGMP dependent activation of cAMP-dependent protein kinase.
据推测，硝基血管扩张剂通过代谢为一氧化氮来诱导平滑肌松弛，一氧化氮随后激活可溶性鸟苷酸环化酶，增加[cGMP]，并激活cGMP依赖性蛋白激酶。然后有人提出，cGMP依赖性磷酸化可降低细胞内Ca2+并降低收缩的Ca(2+)敏感性。我们推测，Ca(2+)敏感性降低的一个组成部分，即肌球蛋白轻链磷酸化的Ca(2+)敏感性降低，是由于肌球蛋白轻链激酶(MLCK)在肽位点A的磷酸化所致。在猪颈动脉中，组胺(10 microM)刺激增加了水母发光蛋白估计的[Ca2+]i、MLCK位点A磷酸化、MLC磷酸化和张力。随后向组胺刺激的组织中添加100 microM硝酸甘油(NTG)或100 microM硝普钠(NP)可增加[cGMP]，降低MLC磷酸化和张力，但未显著改变[cAMP]、[Ca2+]i或MLCK位点A磷酸化。单独向未刺激的组织中添加NTG和NP可增加MLCK位点A磷酸化，但未改变[Ca2+]i。在预先用NP孵育的组织中，与对照组相比，随后的组胺收缩减慢，然而，这种收缩减慢似乎是由于组胺依赖性[Ca2+]i增加的减弱所致。这些数据表明，在猪颈动脉中，硝基血管扩张剂可降低MLC磷酸化的Ca(2+)敏感性，而不增加MLCK位点A磷酸化。硝基血管扩张剂本身可诱导位点A MLCK磷酸化，可能是通过cGMP依赖性激活cAMP依赖性蛋白激酶来实现的。
