Ionic conductances of extracellular shunt pathway in rabbit ileum. Influence of shunt on transmural sodium transport and electrical potential differences.
Ionic conductances of extracellular shunt pathway in rabbit ileum. Influence of shunt on transmural sodium transport and electrical potential differences.
复制标题
兔回肠细胞外分流途径的离子电导。分流对透壁钠转运和电势差的影响。
DOI：
10.1085/jgp.59.3.318
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发表时间：
1972-03
期刊：
影响因子：
--
通讯作者：
Schultz SG
中科院分区：
文献类型：
--
作者：
Frizzell RA;Schultz SG
Na、K和Cl的单向流入兔回肠的分离条是由穿过上皮细胞的粘膜运动和离子扩散到细胞外分流途径组成的。很大一部分钠离子仅通过粘膜流入就被Li抑制，提示在流入过程中有载体机制参与。Na、K和Cl的部分离子分流电导至少占总组织电导的82%。计算的分流导通率(P)为（厘米/小时）P K = 0.040, P Na = 0.035, P Cl = 0.019，则P K:P Na:P Cl = 1.14:1.00:0.55。由甘露醇或KCl等渗替代粘膜溶液中的NaCl引起的组织间扩散电位由Goldman常场方程与上述分流通路的渗透性一起描述。这些观察结果与通过固定电荷孔的渗透不一致，但可以用一个模型来解释，该模型具有恒定的离子分配到穿过紧密结的中性极性孔中。这样的孔可以内衬固定偶极或定向的固定偶极离子，使得电负性基团影响扩散途径的过选择性。这两种模型的基本特征是电中性是通过固定的膜组分来维持的，而不依赖于移动反离子的存在。
The unidirectional influxes of Na, K, and Cl into isolated strips of rabbit ileum are comprised of movements across the mucosal membrane of the epithelial cells and ionic diffusion into an extracellular shunt pathway. A large fraction of the Na influx across the mucosal membrane alone is inhibited by Li, suggesting the participation of a carrier mechanism in the influx process. The partial ionic shunt conductances of Na, K, and Cl account for at least 82% of the total tissue conductance. The calculated shunt permeabilities (P) are (in centimeters per hour) P K = 0.040, P Na = 0.035, and P Cl = 0.019, so that P K:P Na:P Cl = 1.14:1.00:0.55. Diffusion potentials across the tissue resulting from isotonic replacement of NaCl in the mucosal solution with mannitol or KCl are described by the Goldman constant-field equation together with the above permeabilities of the shunt pathway. These observations are not consistent with permeation through a fixed-charge pore but can be explained by a model featuring constant ionic partition into a neutral-polar pore that traverses the tight junction. Such a pore may be lined with either fixed dipoles or fixed dipolar ions oriented such that electronegative groups influence the permselective properties of the diffusion pathway. The essential feature of both models is that electroneutrality is maintained by means of fixed membrane components and does not depend upon the presence of mobile counterions.