Baerlocher K E, Scriver C R, Mohyuddin F
Proc Natl Acad Sci U S A. 1970 Apr;65(4):1009-16. doi: 10.1073/pnas.65.4.1009.
Renal tubular absorption of proline, hydroxyproline, and glycine by the newborn of most mammals is inefficient compared to that of the adult. Cortex slices from seven-day-old rat kidney also transport proline and glycine at reduced initial rates compared to mature kidney. Nonetheless, newborn slices achieve higher intracellular concentrations during prolonged incubation; the latter reflects a reduced rate of efflux, a characteristic peculiar to the membrane of postnatal kidney. The postnatal reduction of initial uptake rates is observed clearly only at substrate concentrations in or below the physiological range; it correlates with the absence of two high-affinity systems which normally serve proline and glycine transport independently at these concentrations in mature kidney, in conjunction with a "common" low-affinity system. The low-affinity system alone performs the observed uptake in the newborn kidney. Specific activity of the high-affinity systems for proline and glycine increases asynchronously after birth, suggesting independent genetic control of the three systems for iminoglycine transport in mammalian kidney.
与成年哺乳动物相比，大多数哺乳动物新生儿对脯氨酸、羟脯氨酸和甘氨酸的肾小管吸收效率较低。与成熟肾脏相比，7日龄大鼠肾脏的皮质切片对脯氨酸和甘氨酸的转运初始速率也较低。尽管如此，新生儿切片在长时间孵育期间能达到更高的细胞内浓度；后者反映了流出速率的降低，这是出生后肾脏膜特有的特征。仅在生理范围或低于生理范围的底物浓度下，才能清楚地观察到出生后初始摄取速率的降低；这与成熟肾脏中通常在这些浓度下独立发挥脯氨酸和甘氨酸转运作用的两个高亲和力系统的缺失有关，同时还与一个“共同”的低亲和力系统有关。在新生肾脏中，仅低亲和力系统进行了观察到的摄取。出生后，脯氨酸和甘氨酸高亲和力系统的比活性异步增加，这表明哺乳动物肾脏中三种亚氨基甘氨酸转运系统受独立的基因控制。
