Fu B M, Weinbaum S, Tsay R Y, Curry F E
Department of Mechanical Engineering, City College, City University of New York, NY 10031.
J Biomech Eng. 1994 Nov;116(4):502-13. doi: 10.1115/1.2895802.
The recent serial section electron microscopic studies by Adamson and Michel (1993) on microves gels of frog mesentery have revealed that the large pores in the junction strand of the interendothelial cleft are widely separated 150 nm wide orifice-like breaks whose gap height 20 nm is the same as the wide part of the cleft. In this paper a modified version of the model in Weinbaum et al. (1992) is first developed in which this orifice structure is explored in combination with a random or ordered fiber matrix layer that is at the luminal surface and/or occupies a fraction of the wide part of the cleft. This basic orifice model predicts that for the measured Lp to be achieved the fiber layer must be confined to a relatively narrow region at the entrance to the cleft where it serves as the primary molecular filter. The model provides a much better fit of the permeability P for intermediate size solutes between 1 and 2 nm radius than the previous model in Weinbaum et al., where the junction strand breaks were treated as finite depth circular or rectangular pores, but like the previous model significantly underestimates P for small ions. However, it is shown that if a small frequent pore of 1.5 nm radius with characteristic spacing comparable to the diameter of the junction proteins or a continuous narrow slit of approximately 1.5 to 2.3 nm gap height is also present in the continuous part of the junction strand, small ion permeability can also be satisfied. The 1.5 nm radius pore does not significantly change Lp, whereas the continuous narrow slit provides a contribution to Lp that is comparable to, or in the case of the 2.3 nm slit greater than, the widely spaced 150 nm orifices. Thus, for the narrow slit the contribution to Lp from the orifices can be as low as 1.0 x 10(-7) cm/s/cm H2O and it is also possible to satisfy the 2.5 fold increase in permeability that occurs when the matrix is enzymatically removed from the luminal side of the cleft, Adamson (1990). The likelihood of each of these cleft structures is discussed.
亚当森和米歇尔（1993年）最近对青蛙肠系膜微血管凝胶进行的系列切片电子显微镜研究表明，内皮间裂隙连接链中的大孔隙是间隔很宽的150纳米宽的孔状断裂，其间隙高度20纳米与裂隙的宽部分相同。在本文中，首先对温鲍姆等人（1992年）的模型进行了改进，在该模型中，结合位于管腔表面和/或占据裂隙宽部分一部分的随机或有序纤维基质层，对这种孔结构进行了探索。这个基本的孔模型预测，为了达到测量的水通透系数（Lp），纤维层必须限制在裂隙入口处相对较窄的区域，在那里它作为主要的分子过滤器。与温鲍姆等人之前的模型相比，该模型对半径在1至2纳米之间的中等大小溶质的渗透率（P）拟合得更好，在之前的模型中，连接链断裂被视为有限深度的圆形或矩形孔，但与之前的模型一样，对小离子的P值显著低估。然而，研究表明，如果在连接链的连续部分还存在半径为1.5纳米、特征间距与连接蛋白直径相当的小而频繁的孔，或者存在间隙高度约为1.5至2.3纳米的连续窄缝，那么小离子的渗透率也可以得到满足。半径为1.5纳米的孔不会显著改变Lp，而连续窄缝对Lp的贡献与间隔很宽的150纳米孔相当，或者在2.3纳米窄缝的情况下大于150纳米孔。因此，对于窄缝，孔对Lp的贡献可以低至1.0×10⁻⁷厘米/秒/厘米H₂O，并且也有可能满足当基质从裂隙管腔侧酶解去除时渗透率增加2.5倍的情况，亚当森（1990年）。讨论了这些裂隙结构中每一种存在的可能性。
