Saumon G, Martet G
Institut National de la Santé et de la Recherche Médicale U82, Faculté Xavier Bichat, Paris, France.
Am J Physiol. 1996 Feb;270(2 Pt 1):L191-8. doi: 10.1152/ajplung.1996.270.2.L191.
The role of the pulmonary sodium-glucose cotransport is unknown. We hypothesized that altering glucose balance (the level of passive vs. active transport) across the airspace epithelium might affect luminal liquid clearance (Jw). A mathematical model was developed to calculate Jw from the rate of epithelial glucose uptake and paracellular permeability. The model predicted that steady-state luminal glucose concentration in fluid-filled lungs should be very low (< 0.5 mM, plasma concentration being 10 mM) and that selective changes in paracellular permeability might affect Jw. Protamine was used to increase paracellular permeability in fluid-filled isolated rat lungs. Protamine modified the glucose equilibrium across the epithelium and increased Jw (P < 0.001) in lungs instilled with fluid that contained no glucose. This increase was accurately described by the model (R2 = 0.92). Jw increased because the entry into airspaces of one glucose molecule and its reuptake results in the net absorption of four osmolytes as long as the cotransport has Na-to-glucose stoichiometry of 2:1, operates below saturation, and the barrier selectivity is preserved. Thus modulating paracellular permeability to small solutes might aid in the removal of edema fluid and participate in the regulation of epithelial lining fluid volume and composition.
肺钠葡萄糖共转运的作用尚不清楚。我们推测，改变气腔上皮细胞的葡萄糖平衡（被动转运与主动转运的水平）可能会影响管腔液体清除率（Jw）。我们建立了一个数学模型，根据上皮细胞葡萄糖摄取率和细胞旁通透性来计算Jw。该模型预测，充满液体的肺中管腔葡萄糖的稳态浓度应非常低（<0.5 mM，血浆浓度为10 mM），并且细胞旁通透性的选择性变化可能会影响Jw。我们使用鱼精蛋白来增加充满液体的离体大鼠肺中的细胞旁通透性。鱼精蛋白改变了上皮细胞的葡萄糖平衡，并增加了注入不含葡萄糖液体的肺中的Jw（P < 0.001）。该模型准确地描述了这种增加（R2 = 0.92）。Jw增加是因为只要共转运的钠与葡萄糖化学计量比为2:1、在饱和状态以下运行且屏障选择性得以保留，一个葡萄糖分子进入气腔并被重新摄取就会导致四个渗透溶质的净吸收。因此，调节对小分子溶质的细胞旁通透性可能有助于清除水肿液，并参与调节上皮衬液的体积和成分。
