Theodore J, Robin E D, Gaudio R, Acevedo J
Am J Physiol. 1975 Oct;229(4):989-96. doi: 10.1152/ajplegacy.1975.229.4.989.
The in vivo transalveolar transport of three large polar solutes, sucrose, inulin, and dextran (mol wt 60,000-90,00), was compared with the transport of urea in saline-filled dog lung. Apparent permeability coefficents (p', in cm X sec-1 X 10(6)) were as follows; urea: 2.4 +/- 0.28 (SD) greater than sucrose: 0.64 +/- 0.31 (P less than 0.001) greater than inulin: 0.12 +/- .05 (P less than 0.001)--not different from dextran (mol wt 60,000-90,000): 0.08 +/- .02 (P greater then .01). Calculation of the resistance of the alveolar epithelium compared to total barrier resistance for the various solutes indicates that approximately 90% of the total resistance resides in the alveolar epithelium. Comparison of the ratio of permeability coefficients to the ratio of free-diffusion coefficients in water shows similar values for the three large polar solutes, suggesting that permeation through the alveolar epithelium occurs by means of water-filled channels. The values for permeability coefficients of alveolar epithelium fit into the spectrum of values reported for other epithelial structures (including gall bladder, frog skin, and toad bladder); it seems to have a system of channels with a small number of wide "pores" (greater than 80 A) that permit permeation of large polar solutes and is not a relatively homogeneous structure.
将三种大分子极性溶质（蔗糖、菊粉和右旋糖酐（分子量60,000 - 90,000））在体内经肺泡的转运与充满生理盐水的犬肺中尿素的转运进行了比较。表观渗透系数（p'，单位为cm×sec⁻¹×10⁶）如下：尿素：2.4±0.28（标准差）大于蔗糖：0.64±0.31（P＜0.001）大于菊粉：0.12±0.05（P＜0.001），与右旋糖酐（分子量60,000 - 90,000）无差异：0.08±0.02（P＞0.01）。计算各种溶质的肺泡上皮阻力与总屏障阻力之比表明，总阻力的约90%存在于肺泡上皮中。比较渗透系数与水中自由扩散系数的比值发现，三种大分子极性溶质的该比值相似，这表明通过肺泡上皮的渗透是借助充满水的通道进行的。肺泡上皮的渗透系数值符合其他上皮结构（包括胆囊、蛙皮和蟾蜍膀胱）报道的值的范围；它似乎有一个具有少量宽“孔”（大于80 Å）的通道系统，允许大分子极性溶质渗透，并且不是一个相对均匀的结构。
