Developmental aspects of proline transport in rat renal brush border membranes.

Abstract

Proline uptake by rat renal brush border membrane vesicles from animals 7 days of age and older has been examined to delineate developmental changes in membrane function that may underlie the physiological hyperprolinuria of young animals. Although the two proline transport systems normally present in adult membranes were found in membranes from young animals, the proline "overshoot" resulting from a sodium ion gradient is minimal and increases with age of the animal from which the membranes were isolated. This is associated with a severalfold faster entry of 22Na into vesicles of the 7-day-old animal compared to entry into membranes prepared from adult kidneys. The very rapid dissipation of the sodium gradient thus diminishing the driving force for transmembrane proline movement may explain the changes in proline overshoot observed in membranes from young animals. The altered sodium permeability is consistent with the fact that young animals have a generalized inability to reabsorb other amino acids whose transport is known to be sodium gradient stimulated.Urinary hyperexcretion of proline and indeed of most amino acids is characteristic ofneonatal rat (1), dog (2), and man (3). Subsequent postnatal development of the nephron, however, reduces urinary amounts of these acids to much lower levels (4, 5). Although the subject of numerous investigations (6-9), the nature of the developmental changes occurring in the kidney that result in decreased amino acid excretion is as yet undefined. An understanding of these changes should not only increase our knowledge of normal transport processes but also provide insight into human disorders of renal amino acid transport, such as familial iminoglycinuria, in which the affected individual continues to excrete excessive quantities of certain amino acids in the urine.Previous studies of the development of renal amino acid transport in rat have relied upon the use of the cortical slice (10, 11) and isolated renal tubule fragment (1,8). Data obtained from these models, however, are influenced by factors such as bidirectional solute movement, substrate penetration, and substrate metabolism. The use of isolated membrane vesicles obviates these problems and age-related differences in solute transport by these vesicles may be examined directly.In our recent studies, proline uptake by renal brush border membrane vesicles prepared from newborn rats by free-flow electrophoresis, unlike vesicles from adult animals, did not show a Na+-gradient-stimulated overshoot but did exhibit a Na+-gradient-enhanced rate of early proline entry (12). To better understand the events accompanying the maturation of renal solute transport we have therefore examined characteristics of proline and Na+ uptake by renal brush border membrane vesicles prepared from rats of various ages ranging from 1 week oflife to adulthood. The results indicate that, although the two proline transport systems normally present in adult membranes are also found in membranes from young animals, the proline overshoot re...

Identification of Mammalian Proline Transporter SIT1 (SLC6A20) with Characteristics of Classical System Imino

“…The K 0.5 for proline (ϳ0.2 mM) for rat SIT1 is similar to the K m values reported for System IMINO (ϳ0.3 mM) (2,5). SIT1-mediated Na ϩ -dependent imino acid transport is stereoselective and Cl Ϫ -stimulated, as described for System IMINO in intestinal and renal brush-border membrane preparations and in choroid plexus (1)(2)(3)(4)(5). Rat SIT1 is a ϳ66-kDa membrane glycoprotein and is the product of the slc6a20 gene, which has a coding region of 1848 bp.…”

“…Tissue Distribution and Substrate Profile of SIT1 Support a Primary Role in Epithelial Transport of Proline-Classical System IMINO activity has been described in brush-border preparations from intestine and kidney (1)(2)(3)(4)(5). Quantitative RT-PCR (RT-qPCR) and in situ hybridization revealed SIT1 expression throughout the gastrointestinal tract and in S 3 segments of the proximal renal tubule (Figs.…”

“…The classically described System IMINO mediates the Na ϩ -dependent transport of imino acids such as proline and pipecolate in a variety of intact tissue and membrane vesicle preparations, including intestine, choroid plexus, and kidney (1)(2)(3)(4)(5). System IMINO does not accept cationic amino acids or non-␣-amino acids.…”

Maturational Effects of Glucocorticoids on Neonatal Brush-Border Membrane Phosphate Transport

“…In both the rabbit (4) and rat (38,40) an increase occurs in the fluorescence anisotropy of DPH (i .e. a decrease in membrane fluidity) in adult as compared with neonatal renal 88M.…”

Ontogeny of Na/H antiporter activity in rabbit renal brush border membrane vesicles.

“…A similar finding has been observed in other developmental studies. Passive Na' conductance in both renal (52) and intestinal (53) BBMV is higher in young compared to adult animals. Because the Na/K ATPase is not fully developed in these immature animals (6), the increased conductance for Na' in young animals could result in intracellular accumulation of Na' and a reduction in the gradient for Na' across the luminal membrane.…”