DELINEATION OF SEPARATE TRANSPORT SYSTEMS IN RAT KIDNEY CORTEX FOR L-LYSINE AND L-CYSTINE BY DEVELOPMENTAL PATTERNS

L-Cystine uptake by newborn rat kidney cortex in vitro is impaired and does not reach the normal adult level until fifteen days of age. L-lysine uptake by young cortex, on the other hand, is comparable to that observed in adults. Exchange diffusion of lysine in the newborn's cortex is also similar to adult tissue. Cystine uptake by newborn cortex is impaired further with sodium deprivation while that of lysine is markedly increased in the absence of sodium. These developmental differences argue against the concept of a common transport process for these two amino acids. © 1969.