Rembold C M, O'Connor M
Cardiovascular Division, Departments of Internal Medicine and Physiology, University of Virginia Health System, Charlottesville, VA 22908, USA.
Biochim Biophys Acta. 2000 Mar 17;1500(3):257-64. doi: 10.1016/s0925-4439(99)00112-x.
Nitrovasodilators, high extracellular Mg(2+), and some other relaxing agents can cause smooth muscle relaxation without reductions in myosin regulatory light chain (MRLC) phosphorylation. Relaxations without MRLC dephosphorylation suggest that other regulatory systems, beyond MRLC phosphorylation, are present in smooth muscle. We tested whether changes in caldesmon phosphorylation, heat shock protein 20 (HSP20) phosphorylation, or intracellular pH (pH(i)) could be responsible for relaxation without MRLC dephosphorylation. In unstimulated tissues, caldesmon was phosphorylated 1.02+/-0.10 mol P(i)/mol caldesmon (mean+/-1 S.E.M.), HSP20 was phosphorylated 0.005+/-0.003 mol P(i)/mol HSP20, and estimated pH(i) was 7.21+/-0.07. Histamine stimulation induced a contraction, an intracellular acidosis, but did not significantly change caldesmon or HSP20 phosphorylation. Addition of nitroglycerin induced a relaxation, significantly increased HSP20 phosphorylation to 0.18+/-0.02 mol P(i)/mol HSP20, did not significantly change caldesmon phosphorylation, and pH(i) returned to near unstimulated values. Increase in extracellular Mg(2+) to 10 mM induced a relaxation, but did not significantly change HSP20 or caldesmon phosphorylation. These data suggest that changes in caldesmon phosphorylation, HSP20 phosphorylation, or pH(i) cannot be the sole explanation for relaxation without MRLC dephosphorylation. However, it is possible that HSP20 phosphorylation may be involved in nitroglycerin-induced relaxation without MRLC dephosphorylation.
硝基血管扩张剂、高细胞外镁离子（Mg²⁺）以及其他一些舒张剂可引起平滑肌舒张，而肌球蛋白调节轻链（MRLC）磷酸化并无降低。无MRLC去磷酸化的舒张表明，除MRLC磷酸化外，平滑肌中还存在其他调节系统。我们测试了钙调蛋白磷酸化、热休克蛋白20（HSP20）磷酸化或细胞内pH值（pH(i)）的变化是否可能是无MRLC去磷酸化舒张的原因。在未受刺激的组织中，钙调蛋白的磷酸化水平为1.02±0.10摩尔无机磷（P(i)）/摩尔钙调蛋白（平均值±1标准误），HSP20的磷酸化水平为0.005±0.003摩尔P(i)/摩尔HSP20，估计的pH(i)为7.21±0.07。组胺刺激引起收缩和细胞内酸中毒，但未显著改变钙调蛋白或HSP20的磷酸化。添加硝酸甘油引起舒张，显著增加HSP20磷酸化至0.18±0.02摩尔P(i)/摩尔HSP20，未显著改变钙调蛋白磷酸化，且pH(i)恢复至接近未受刺激时的值。细胞外Mg²⁺增加至10 mM引起舒张，但未显著改变HSP20或钙调蛋白磷酸化。这些数据表明，钙调蛋白磷酸化、HSP20磷酸化或pH(i)的变化不能是无MRLC去磷酸化舒张的唯一解释。然而，HSP20磷酸化可能参与了硝酸甘油诱导的无MRLC去磷酸化舒张。
