Moran W M, Garretson L T
Department of Physiology and Cell Biology, University of Texas Medical School, Houston 77225.
Am J Physiol. 1988 Oct;255(4 Pt 2):R583-90. doi: 10.1152/ajpregu.1988.255.4.R583.
We have reexamined the notion that sugars stimulate ion absorption differently in invertebrate and vertebrate intestine. In the seahare intestine, mucosal sugar presumably increases the rate of transcellular Na+ and Cl- absorption, whereas only transcellular Na+ absorption is increased in the vertebrate small intestine. Our data indicate that the seahare intestine responds to mucosal D-galactose like the vertebrate small intestine: namely, the apical membrane electrical potential difference depolarizes, the ratio of the mucosal to serosal membrane resistances decreases, and the short-circuit current (Isc) increases. Because mucosal substitution of tetramethylammonium for Na+ abolished the increased Isc, this stimulation resulted from an increase in rheogenic Na+ absorption. Unidirectional transepithelial Cl- fluxes indicate that mucosal D-galactose had no effect on the net Cl- flux under short-circuit conditions. Further, ion substitution experiments indicate that the apical membrane is K+ conductive rather than Cl- conductive as previously reported. These electrophysiological as well as parallel histological findings indicate that studies previously reported on the seahare intestine were in fact conducted on the esophagus.
我们重新审视了糖类在无脊椎动物和脊椎动物肠道中对离子吸收有不同刺激作用这一观点。在海兔肠道中，黏膜糖类大概会增加跨细胞的Na⁺和Cl⁻吸收速率，而在脊椎动物小肠中只有跨细胞的Na⁺吸收会增加。我们的数据表明，海兔肠道对黏膜D - 半乳糖的反应与脊椎动物小肠类似：即顶端膜电位差去极化，黏膜膜与浆膜电阻之比降低，短路电流（Isc）增加。由于用四甲基铵替代Na⁺的黏膜替代消除了增加的Isc，这种刺激是由生电Na⁺吸收增加引起的。单向跨上皮Cl⁻通量表明，在短路条件下黏膜D - 半乳糖对净Cl⁻通量没有影响。此外，离子替代实验表明，顶端膜是K⁺传导性的，而不是如先前报道的Cl⁻传导性的。这些电生理以及平行的组织学发现表明，先前报道的关于海兔肠道的研究实际上是在食管上进行的。
