Crane J M, Hall S B
Departments of Biochemistry and Molecular Biology, Medicine, and Physiology and Pharmacology, Oregon Health Sciences University, Portland, Oregon 97201-3098, USA.
Biophys J. 2001 Apr;80(4):1863-72. doi: 10.1016/S0006-3495(01)76156-5.
Films of pulmonary surfactant in the lung are metastable at surface pressures well above the equilibrium spreading pressure of 45 mN/m but commonly collapse at that pressure when compressed in vitro. The studies reported here determined the effect of compression rate on the ability of monolayers containing extracted calf surfactant at 37 degrees C to maintain very high surface pressures on the continuous interface of a captive bubble. Increasing the rate from 2 A(2)/phospholipid/min (i.e., 3% of (initial area at 40 mN/m)/min) to 23%/s produced only transient increases to 48 mN/m. Above a threshold rate of 32%/s, however, surface pressures reached > 68 mN/m. After the rapid compression, static films maintained surface pressures within +/- 1 mN/m both at these maximum values and at lower pressures following expansion at < 5%/min to > or = 45 mN/m. Experiments with dimyristoyl phosphatidylcholine at 37 degrees C produced similar results. These findings indicate that compression at rates comparable to values in the lungs can transform at least some phospholipid monolayers from a form that collapses readily at the equilibrium spreading pressure to one that is metastable for prolonged periods at higher pressures. Our results also suggest that transformation of surfactant films can occur without refinement of their composition.
肺表面活性物质在肺内形成的薄膜在远高于45 mN/m的平衡铺展压力的表面压力下是亚稳态的，但在体外压缩时通常在该压力下会塌陷。本文报道的研究确定了压缩速率对含有从37℃小牛提取的表面活性剂的单层在俘获气泡的连续界面上维持非常高表面压力能力的影响。将速率从2 Ų/磷脂/分钟（即40 mN/m时初始面积的3%/分钟）提高到23%/秒仅使表面压力短暂升高至48 mN/m。然而，高于32%/秒的阈值速率时，表面压力达到>68 mN/m。快速压缩后，静态薄膜在这些最大值以及以<5%/分钟膨胀至≥45 mN/m后的较低压力下，都能将表面压力维持在±1 mN/m范围内。在37℃下用二肉豆蔻酰磷脂酰胆碱进行的实验产生了类似的结果。这些发现表明，以与肺内值相当的速率进行压缩可以使至少一些磷脂单层从在平衡铺展压力下容易塌陷的形式转变为在较高压力下长时间保持亚稳态的形式。我们的结果还表明，表面活性剂薄膜的转变可以在不改善其组成的情况下发生。
