Development Aspects of Renal β-Amino Acid Transport. V Brush Border Membrane Transport in Nursing Animals—Effect of Age and Diet

Abstract

ABSTRACT. This study examines the Na+-dependent accumulation of the &amino acid, taurine, by brush border membrane vesicles isolated from nursing animals compared to uptake in adult animals. The diets fed to the mothers nursing these pups were altered so as to provide a low sulfur amino acid intake or a high taurine diet as well as conventional sulfur amino acid intake. Taurinuria is greater in nursing animals than in adult controls, but animals of all ages respond to exposure to the low sulfur amino acid intake by conservation of taurine and to the high taurine diet by hyperexcretion of taurine. Taurine uptake at 10 pM by brush border membrane vesicles is influenced by age in all groups and by diet in 14-and 21-day-old animals. A precession of uptake is seen both in terms of initial and peak rate of uptake with the lowest values in 7-day-old animals to the highest in adult. Greater brush border membrane vesicle uptake is found in 14-and 21-day-old rats after exposure to the low sulfur amino acid intake and reduced uptake after the HTD, whereas no dietary influence on uptake was found in 7-day-old rats. Neither the pattern of the time course of uptake nor the uptake values at equilibrium (45 min) are affected by age or diet. Kinetic analyses of concentration dependent uptake show that the maturational process involves a change in the Vmax of initial uptake. Kinetic analysis of the adaptive response reveals an increase in Vmax after low sulfur amino acid intake and a decline after high taurine diet in 14-and 21-day-old pups, but not in 7-day-old pups. Uptakes at high taurine concentrations (5 mM) which are 10-fold higher than the Km are uninfluenced by age or diet. This study indicates that the physiologic taurinuria of immature rats may relate, in part, to a lower rate of uptake at the brush border surface, but that after 1 wk and before 2 wk of age the kidney can adapt to changes in sulfur amino acid intake. (Pediatr Res 202390-894,1986 The renal tubular epithelium is involved in the reabsorption of various ions and nutrients, including amino acids that arise by virtue of filtration across the glomerular basement membrane. A "physiologic" aminoaciduria is evident in the young of all mammalian species. On the surface, aminoaciduria seems inappropriate in view of the need for a young, rapidly growing animal to conserve compounds that are important in growth (I, 2). Our lab has been concerned with those factors that contribute to the development of amino acid transport processes in the maturing animal and we hope to understand more fully whether maturation of the transport process can be accelerated by various physiologic manipulations (3-7). We have used as a transport probe, the p-amino acid, taurine, since one can manipulate the dietary intake of sulfur amino acids which results in a renal adaptive response for taurine (5,(8)(9)(10)(11)(12)(13).Full grown rats fed a limited sulfur amino acid intake reduce their urinary taurine excretion, a finding which is paralleled in vitro by augmented uptake of taurine by c...

Developmental Aspects of Renal β-Amino Acid Transport. VI. The Role of Membrane Fluidity and Phospholipid Composition in the Renal Adaptive Response in Nursing Animals

“…In the present study the values for P at the break point were higher than in the other reports. This may relate to the point that our membranes were isolated by calcium chloride precipitation (15), rather than magnesium chloride precipitation (43) or magnesium chloride followed by free flow electrophoresis (44). However, the values for P determined at extreme values (5_15°and 37-56°) were similar in all four studies.…”

“…The uptake of taurine (Na"-dependent component) was greater in BBMV prepared from animals nursed by mothers fed in comparison to animals whose mothers were fed the NTD at 14 and 21 days of age (15). Similarly, the uptake of taurine is diminished in HTD exposed pups at ages 14 and 21 days.…”

“…At 7 days no difference in uptake is found. These results are presented elsewhere (15) but are mentioned since the membranes prepared for these transport studies were also used to measure membrane fluidity and phospholipid composition herein. Thus, the membrane samples being evaluated demonstrate directly the renal adaptive response to diet, at least 14, 21, and adult membranes.…”

“…The Na"-dependent accumulation of taurine by BBMV isolated from nursing animals shows enhanced uptake in BBMV prepared from pups whose mothers art. fed a LTD and reduced in membranes from pups fed a HTD when compared to membranes from pups whose dams were fed a NTO (15). Taurinuria is greater in nursing or weanling pups as compared to adult controls, but animals of all ages (7, 14, 21, 28 day and adult) respond to exposure to the LTO by urinary conservation of taurine and to the HTD by hyperexcretion of this l3-amino acid (5,15).…”

“…BBMV are prepared from kidney cortex by a modification of the calcium chloride precipitation method of Booth and Kenny (24) as described previously (9). The method of preparing BBMV from nursing animals has been described previously (15). The final BBMV pellet was resuspended in 290 mM mannitol, 10 mM Tris/HEPES (pH 7.4) and either used fresh or frozen at -70 0 C. Protein was measured according to Lowry et at.…”