Ishibashi S, Kawasaki K, Tate Y, Ihara T, Shimada K
Tomobe Kokuho Hospital, Ibaraki, Japan.
Experientia. 1995 Sep 29;51(9-10):980-5. doi: 10.1007/BF01921752.
The smooth muscle relaxation induced by nitroglycerin is hypothesized to be mediated by an increase in the cytoplasmic concentration of guanosine 3',5'-monophosphate (cGMP) and subsequent dephosphorylation of the 20-kilodalton myosin light chain (MLC). We investigated this hypothesis in procine coronary arterial smooth muscle stimulated with histamine (3 microM) or K+ (30 mM). Stimulation of [32P]Pi-labeled muscle with histamine or K+ for 2 min resulted in a four- or 6.2-fold increase, respectively, in the incorporation of 32P into MLC. After 48 min of exposure to histamine, MLC phosphorylation decreased to the basal level and the phosphorylation of desmin, synemin, and of three unidentified cytosolic proteins was increased. K+ stimulation resulted in a sustained increase of MLC phosphorylation but had no effect on the phosphorylation of desmin, synemin, or the three unidentified cytosolic proteins. Application of nitroglycerin (1 microM) 48 min after histamine stimulation inhibited the phosphorylation of desmin, synemin, and the three cytosolic proteins. The sustained phase of histamine-induced contraction was also inhibited to a greater extent then the acute phase of histamine-induced contraction and both the acute and sustained phases of K(+)-induced contraction. These results suggest that MLC phosphorylation is required for both phases of K(+)-induced contraction, whereas phosphorylation of intermediate filament proteins is required for the sustained phase of histamine-induced contraction. Intermediate filament proteins, rather than MLC, may also be the target for the relaxant action of nitroglycerin during histamine-induced sustained contraction.
硝酸甘油诱导的平滑肌舒张被认为是由鸟苷 3',5'-单磷酸（cGMP）胞质浓度增加以及随后 20 千道尔顿肌球蛋白轻链（MLC）的去磷酸化介导的。我们在用组胺（3 microM）或 K⁺（30 mM）刺激的猪冠状动脉平滑肌中研究了这一假设。用组胺或 K⁺刺激 [³²P]Pi 标记的肌肉 2 分钟，分别导致 ³²P 掺入 MLC 的量增加了 4 倍或 6.2 倍。暴露于组胺 48 分钟后，MLC 磷酸化降至基础水平，结蛋白、丝连蛋白以及三种未鉴定的胞质蛋白的磷酸化增加。K⁺刺激导致 MLC 磷酸化持续增加，但对结蛋白、丝连蛋白或三种未鉴定的胞质蛋白的磷酸化没有影响。组胺刺激 48 分钟后应用硝酸甘油（1 microM）可抑制结蛋白、丝连蛋白和三种胞质蛋白的磷酸化。组胺诱导收缩的持续期比组胺诱导收缩的急性期受到的抑制程度更大，并且 K⁺诱导收缩的急性期和持续期均受到抑制。这些结果表明，K⁺诱导收缩的两个阶段都需要 MLC 磷酸化，而组胺诱导收缩的持续期需要中间丝蛋白的磷酸化。在组胺诱导的持续收缩过程中，中间丝蛋白而非 MLC 也可能是硝酸甘油舒张作用的靶点。
