Schultz S G
Fed Proc. 1981 Jul;40(9):2408-11.
Studies of the bidirectional fluxes of K across segments of rabbit descending colon indicate that: a) when the tissue is short-circuited, the net flux does not differ significantly from zero under control conditions and in the presence of aldosterone; and b) the bidirectional fluxes of K conform to the Ussing flux-ratio equation over a wide range of transepithelial electrochemical potential differences. These and other findings strongly suggest that the movements of K across the epithelium are restricted to paracellular routes and are entirely passive. Studies dealing with the mechanism of homocellular K transport indicate that: a) K is actively transported into the cells across the basolateral membranes against an electrochemical potential difference of approximately 30 mV; and b) the active uptake of K may be mediated by a rheogenic Na-K exchange pump that is also responsible for transcellular Na transport. These results are entirely consistent with the model proposed by Koefoed-Johnson and Ussing for isolated frog skin.
a）当组织短路时，在对照条件下以及存在醛固酮的情况下，净通量与零无显著差异；b）在广泛的跨上皮电化学势差范围内，钾的双向通量符合乌斯通量比方程。这些以及其他发现强烈表明，钾跨上皮的移动仅限于细胞旁途径，并且完全是被动的。关于同细胞钾转运机制的研究表明：a）钾逆着约30 mV的电化学势差通过基底外侧膜被主动转运到细胞内；b）钾的主动摄取可能由一种生电钠钾交换泵介导，该泵也负责跨细胞钠转运。这些结果与科弗德 - 约翰逊和乌斯为分离的蛙皮提出的模型完全一致。
