McLaughlin G E, Kim K J, Berg M M, Agoris P, Lubman R L, Crandall E D
Cornell University Medical College, New York, NY.
Respir Physiol. 1993 Mar;91(2-3):321-34. doi: 10.1016/0034-5687(93)90109-n.
Most previous studies in isolated perfused lungs have utilized measurements of solute flow from alveolar to vascular space to characterize the barrier and transport properties of the alveolar epithelium. In this study, we measured flux of a series of nonionic hydrophilic solutes and sodium across the alveolar epithelium of the isolated rat lung from perfusate to airspace (P-->A), as well as from airspace to perfusate (A-->P). Apparent permeability-surface area products (PS) were calculated from the rates of isotope appearance downstream in either the airspace or the perfusate. Equivalent pore analysis of data for P-->A solute flow demonstrated a small pore population with radius 0.6 nm occupying 85% of the total pore area and a large pore population with radius 3.8 nm occupying 15% of the total area. Similar analysis of A-->P solute flux demonstrated a small pore population of 0.6 nm occupying 86% of the total pore area and a large pore population with radius 2.9 nm occupying 14% of total pore area. The ratio (R) of PSP-->A divided by PSA-->P was 0.8 for the nonionic hydrophilic solutes, while R for sodium was 0.5. In the presence of amiloride and ouabain, R for sucrose was unchanged while R for sodium increased to 0.8 due to a fall in PSA-->P. The difference between R for sodium and R for the passively transported solutes, and the reduction in this difference in the presence of sodium transport inhibitors, are consistent with active sodium reabsorption by the intact alveolar epithelium. Differences in measured unidirectional passive solute fluxes probably result from unequal effective surface areas for diffusion from vascular space to airspace and vice versa in the anatomically complex mammalian lung.
以往大多数关于离体灌注肺的研究都利用溶质从肺泡腔到血管腔的流量测量来表征肺泡上皮的屏障和转运特性。在本研究中，我们测量了一系列非离子亲水性溶质和钠从灌注液到气腔（P→A）以及从气腔到灌注液（A→P）穿过离体大鼠肺泡上皮的通量。表观通透率-表面积乘积（PS）根据气腔或灌注液中下游同位素出现的速率计算得出。对P→A溶质流量数据的等效孔分析表明，半径为0.6 nm的小孔群体占总孔面积的85%，半径为3.8 nm的大孔群体占总面积的15%。对A→P溶质通量的类似分析表明，半径为0.6 nm的小孔群体占总孔面积的86%，半径为2.9 nm的大孔群体占总孔面积的14%。非离子亲水性溶质的PSP→A除以PSA→P的比值（R）为0.8，而钠的R为0.5。在存在氨氯吡脒和哇巴因的情况下，蔗糖的R不变，而由于PSA→P下降，钠的R增加到0.8。钠的R与被动转运溶质的R之间的差异，以及在存在钠转运抑制剂时这种差异的减小，与完整肺泡上皮对钠的主动重吸收一致。所测量的单向被动溶质通量的差异可能是由于在解剖结构复杂的哺乳动物肺中，从血管腔到气腔以及反之从气腔到血管腔的扩散有效表面积不相等所致。
