Frizzell R A, Turnheim K
J Membr Biol. 1978 May 3;40(3):193-211. doi: 10.1007/BF02002968.
The unidirectional influx of Na from the mucosal solution into the epithelium of in vitro descending rabbit colon (JName) determined under short-circuit conditions, is comprised of two components: one represents entry of Na into transporting epithelial cells and is abolished by amiloride which also abolishes Na absorption (JNanet). The other represents diffusional Na entry into paracellular pathways traversing the epithelium. In all instances, exposure of the mucosal surface to amphotericin B increased tissue conductance and JName and elicited K secretion. Tissues showing a spontaneous Isc of approximately 4 microneq/cm2hr did not respond to amphotericin B with increased Isc and JNanet. However, in tissues characterized by a lower Isc under control conditions, amphotericin B increased Isc and JNanet to approximately 4 microneq/cm2 hr. These findings suggest that amphotericin increases JNanet and elicits K secretion by disrupting the normal perm-selectivity of the mucosal membrane. Under these conditions the extrusion of Na from cell-to-serosal solution becomes the rate limiting step in transepithelial Na transport. Finally, a close correlation between JName and JNanet was was observed when the rate of Na absorption varied either spontaneously or experimentally with amiloride, suggesting that the backflux of Na from cell-to-mucosal solution is undetectably small.
在短路条件下测定的体外兔降结肠黏膜溶液中Na向上皮单向流入量（JName）由两个部分组成：一部分代表Na进入转运上皮细胞，可被氨氯吡咪阻断，氨氯吡咪也会消除Na吸收（JNanet）。另一部分代表Na通过扩散进入穿过上皮的细胞旁途径。在所有情况下，将黏膜表面暴露于两性霉素B会增加组织电导和JName，并引发K分泌。显示自发短路电流（Isc）约为4微当量/平方厘米·小时的组织对两性霉素B没有出现Isc和JNanet增加的反应。然而，在对照条件下Isc较低的组织中，两性霉素B使Isc和JNanet增加到约4微当量/平方厘米·小时。这些发现表明，两性霉素通过破坏黏膜膜的正常通透选择性增加JNanet并引发K分泌。在这些条件下，Na从细胞向浆膜溶液的挤出成为跨上皮Na转运的限速步骤。最后，当Na吸收速率自发变化或用氨氯吡咪进行实验性改变时，观察到JName和JNanet之间存在密切相关性，这表明从细胞到黏膜溶液的Na回流小到无法检测。
