Renal cortex taurine content regulates renal adaptive response to altered dietary intake of sulfur amino acids.

Abstract

Rats fed a reduced sulfur amino acid diet (LTD) or a high-taurine diet (HTD) demonstrate a renal adaptive response. The LTD results in hypotaurinuria and enhanced brush border membrane vesicle (BBMV) accumulation of taurine. The HTD causes hypertaurinuria and reduced BBMV uptake. This adaptation may relate to changes in plasma or renal cortex taurine concentration. Rats were fed a normal-taurine diet (NTD), LTD, or HTD for 14 d or they underwent: (a) 3% /3-alanine for the last 8 d of each diet; (b) Feeding 3% glycine did not alter the plasma, renal cortex, or urinary taurine concentrations, or BBMV uptake of taurine. Feeding 3% methionine raised plasma and urinary taurine excretion but renal tissue taurine was unchanged, as was initial BBMV uptake. Hence, nonsulfur-containing a-amino acids did not change /3-amino acid transport.The increase in BBMV uptake correlates with the decline in renal cortex and plasma taurine content. However, since 3% methionine changed plasma taurine without altering BBMV uptake, it is more likely that the change in BBMV uptake and the adaptive response expressed at the brush border surface relate to changes in renal cortex taurine concentrations.Finally, despite changes in urine and renal cortex taurine content, brain taurine values were unchanged, which suggests that this renal adaptive response maintains stable taurine concentrations where taurine serves as a neuromodulator.

Membrane Fluidity and Phospholipid Composition in Relation to Sulfur Amino Acid Intake in Brush Border Membranes of Rat Kidney

“…This renal adaptive response has been demonstrated for the @-amino acid, taurine, which is conserved following diminished sulfur amino acid intake and hyperexcreted in the urine after dietary taurine excess (1)(2)(3). Studies employing isolated luminal brush border membrane vesicles are consistent with these changes in urinary excretion of taurine occurring as the consequence of a membrane-related event (3,4), since the LTD appears to increase the Vmax of initial Naf-taurine symport and the HTD decrease the Vmax of uptake into vesicles. We conducted these studies to determine if these diets influence the microviscosity and phospholipid composition of these vesicles.…”

“…The composition of the diet is described in detail elsewhere (3,4,17). Briefly each diet (LTD, HTD, or normal taurine diet (NTD)] is isoproteinic and contains soy protein which contains limited amounts of methionine and cysteine.…”

“…Evidence for the adaptive response occurs within 72 h after initiation of diet (1 7) and is completely established within 6 days. Animals consuming the LTD, which is limiting in methionine and cysteine are 13 k 2% smaller at the end of the 14 days (3,4,17). No attempts are made to pair-feed these animals since the LTD-fed group actually ingests more food.…”

“…Determinations were made of membrane y-glutanyl transferase, 5'-nucleotidase, acid phosphatase (pH 4.8), N-acetyl-B-D-glycosaminidase, succinyl-cytochrome C reductase, malate dehydrogenase, DNA, oubain-inhibitable Na+ + K+ ATPase (3,4). Of marker enzymes examined the final membrane preparation contained a 6-to 1 1 -fold increase in specific activity for y-glutamyltranspeptidase and 5'-nucleotidase relative to the starting homogenate and a 1.2-to 1 .4-fold increase in Na+ + K+ ATPase, a marker of basal-lateral membranes.…”

“…The uptake of taurine into brush border membrane vesicles at 23" C was performed and according to our established procedure (3,4). Uptake is Na+ and C1-dependent (2 1) and takes place into an osmotically influenced space, thus accumulation of taurine represents intravesicular uptake (2)(3)(4)21). The internal medium consisted of 278 mM mannitol, 1 mM Mg SO4, and 10 mM Tris/HEPES (pH 7.4) and the uptake medium (external) consisted of 100 mM NaCl, 1 mM MgS04, 10 mM Tris/HEPES (pH 7.4), and 10 pM taurine with 0.5 pCi of 'H-taurine.…”