Moreno R H, Hogg J C, McLean T M, Paré P D
J Appl Physiol (1985). 1987 Jan;62(1):82-90. doi: 10.1152/jappl.1987.62.1.82.
Isovolumetric and isobaric tracheal smooth muscle (TSM) contraction were studied in vitro in a preparation of the whole rabbit trachea. Eight tracheae from New Zealand White rabbits were excised and mounted at a fixed length in an organ bath. Electrical field stimulation (EFS) was performed in isovolumetric and isobaric conditions at varying transmural pressures (TMP). Supramaximal stimulation with methacholine was done at 0 TMP. Active change in pressure (delta P) with EFS showed a peak at 3.1 +/- 1.06 cmH2O TMP during inflation and at 4.1 +/- 1.18 cmH2O TMP during deflation (mean +/- SE). Active delta P decreased at higher or lower TMP. Active change in volume with EFS showed a peak at 3.2 +/- 1.26 cmH2O TMP during inflation and at 1.8 +/- 0.98 cmH2O TMP during deflation. A decrease in response was also observed at higher and lower TMP. From these data, we concluded that TSM is at optimal length (Lmax) at TMP of 2-3 cmH2O. Maximal TSM shortening with supramaximal stimulation with methacholine was 32% Lmax. This figure is considerably smaller than the 80% shortening found in unloaded strips of TSM. We conclude that rabbit TSM length is close to Lmax at TMP similar to those found at functional residual capacity and that the loads that the muscle has to overcome probably contribute to the limited shortening observed in situ.
在整个兔气管标本中对等容和等压气管平滑肌（TSM）收缩进行了体外研究。从新西兰白兔身上切除8段气管，并以固定长度安装在器官浴槽中。在等容和等压条件下，于不同跨壁压力（TMP）下进行电场刺激（EFS）。在0 TMP时用乙酰甲胆碱进行超最大刺激。EFS引起的压力主动变化（ΔP）在充气时于3.1±1.06 cmH₂O TMP处出现峰值，在放气时于4.1±1.18 cmH₂O TMP处出现峰值（均值±标准误）。在更高或更低的TMP时，主动ΔP降低。EFS引起的容积主动变化在充气时于3.2±1.26 cmH₂O TMP处出现峰值，在放气时于1.8±0.98 cmH₂O TMP处出现峰值。在更高和更低的TMP时也观察到反应降低。根据这些数据，我们得出结论，TSM在2 - 3 cmH₂O的TMP时处于最佳长度（Lmax）。用乙酰甲胆碱超最大刺激时TSM的最大缩短为Lmax的32%。该数值明显小于在无负荷的TSM条带中发现的80%的缩短率。我们得出结论，兔TSM长度在与功能残气量时相似的TMP下接近Lmax，并且肌肉必须克服的负荷可能是导致在原位观察到的有限缩短的原因。
