Tuck Stephanie A, Maghni Karim, Poirier Annie, Babu Gopal J, Periasamy Muthu, Bates Jason H T, Leguillette Renaud, Lauzon Anne-Marie
Meakins Christie Laboratories, Department of Medicine, McGill University, 3626 St-Urbain St., Montréal, PQ, H2X 2P2 Canada.
Am J Respir Cell Mol Biol. 2004 Mar;30(3):326-32. doi: 10.1165/rcmb.2003-0254OC. Epub 2003 Sep 4.
Two smooth muscle myosin heavy chain isoforms that differ by the presence ([+]insert) or the absence ([-]insert) of a 7-amino acid insert in the motor domain have a 2-fold difference in their in vitro actin filament velocity. We hypothesized that a preferential expression of the fast (+)insert isoform in airway smooth muscle would increase the rate of bronchoconstriction. To verify our hypothesis we measured the time course of bronchoconstriction following a bolus injection of methacholine (160 microg/kg) in (+)insert isoform knockout (KO) and corresponding wild-type (WT) mice. Neither baseline airway resistance (Raw) (0.424 +/- 0.04 for WT and 0.374 +/- 0.01 cm H(2)O.s.ml(-1) for KO) nor peak Raw (4.1 +/- 0.9 for WT and 4.0 +/- 0.5 cm H(2)O.s.ml(-1) for KO) differed between groups. However, the time to peak Raw was significantly longer in the KO (17.2 +/- 0.6 s) compared with the WT (14.6 +/- 0.8 s) mice (P < 0.05). Differentiating Raw with respect to time revealed a greater rate of bronchoconstriction for the WT during the initial 4 s, presumably reflecting the faster shortening velocities under these relatively unloaded conditions. Reverse transcriptase-polymerase chain reaction analysis revealed that the (+)insert myosin isoform mRNA content in the WT airways was 47.8 +/- 5.6%. We conclude that the presence of the (+)insert myosin isoform in the airways increases the rate of bronchoconstriction.
两种平滑肌肌球蛋白重链亚型在运动结构域中存在（[+]插入）或不存在（[-]插入）一个7氨基酸插入片段，它们在体外肌动蛋白丝速度上有2倍的差异。我们假设气道平滑肌中快速（+）插入亚型的优先表达会增加支气管收缩的速率。为了验证我们的假设，我们在（+）插入亚型敲除（KO）和相应的野生型（WT）小鼠中，测量了大剂量注射乙酰甲胆碱（160微克/千克）后支气管收缩的时间进程。两组之间的基线气道阻力（Raw）（WT为0.424±0.04，KO为0.374±0.01厘米水柱·秒·毫升-1）和峰值Raw（WT为4.1±0.9，KO为4.0±0.5厘米水柱·秒·毫升-1）均无差异。然而，与WT小鼠（14.6±0.8秒）相比，KO小鼠达到峰值Raw的时间显著更长（17.2±0.6秒）（P<0.05）。对Raw关于时间进行微分显示，在最初4秒内WT小鼠的支气管收缩速率更高，这可能反映了在这些相对无负荷条件下更快的缩短速度。逆转录聚合酶链反应分析显示，WT气道中（+）插入肌球蛋白亚型mRNA含量为47.8±5.6%。我们得出结论，气道中存在（+）插入肌球蛋白亚型会增加支气管收缩的速率。
