Hajjar J J, Khuri R N, Curran P F
J Gen Physiol. 1972 Dec;60(6):720-34. doi: 10.1085/jgp.60.6.720.
The exit of alanine across the serosal border of the epithelial cells of turtle intestine was measured by direct and indirect techniques. A decrease or an increase in cell Na did not affect the amino acid flux from cell to serosal solution. Cells loaded with Na and alanine did not exhibit any extrusion of alanine when their serosal membranes were exposed to an Na-free medium containing alanine. However, substantial amino acid extrusion was observed across the mucosal cell border under similar conditions. Although alanine flux across the serosal membrane appeared to be Na-independent, it showed a tendency toward saturation as cellular alanine concentration was elevated. The results are consistent with the postulate that the serosal and mucosal membranes of intestinal cells are asymmetrical with respect to amino acid transport mechanisms. The serosal membrane appears to have an Na-independent carrier-mediated mechanism responsible for alanine transport while transport across the mucosal border involves an Na-dependent process.
通过直接和间接技术测量了丙氨酸穿过龟肠上皮细胞浆膜边界的情况。细胞内钠离子的减少或增加并不影响氨基酸从细胞向浆膜溶液的通量。当浆膜暴露于含丙氨酸的无钠培养基中时，加载了钠离子和丙氨酸的细胞并未表现出丙氨酸的任何外排。然而，在类似条件下，观察到大量氨基酸穿过黏膜细胞边界向外排出。尽管丙氨酸穿过浆膜的通量似乎不依赖于钠离子，但随着细胞内丙氨酸浓度的升高，它呈现出饱和趋势。这些结果与以下假设一致：肠道细胞的浆膜和黏膜在氨基酸转运机制方面是不对称的。浆膜似乎具有一种不依赖于钠离子的载体介导机制来负责丙氨酸的转运，而穿过黏膜边界的转运则涉及一个依赖于钠离子的过程。
