Compartmentation of amino acids in the rat kidney

Amino acid concentrations ([AA]) were determined in cortical, outer and inner medullary (OM and IM), and papillary tissue of rat kidney (C-ti, mmol/kg wet wt), in plasma (C-pl), and in urine. In all regions, C-ti values were highest for Tau, Gly, and Glu(-), making up 54-65% of the total [AA]: 27, 21, and 11 mmol/kg wet wt in cortex, OM, and IM and papilla, respectively. Cortical cell water [AA] values (C-cH2O, mmol/kgH(2)O) were between 12.4 (Tau) and 0.09 (Orn(+)), representing cell water-to-plasma water ratios (C-cH2O/C-pH2O between 134 (Asp(-)) and 0.9 (Thr and Cit). Short-term water diuresis did not change the total tissue [AA] throughout the kidney. Treatment of the tissue with Triton X-100 instead of sulfosalicylic acid (SSA) resulted in much higher [AA], except for Glu(-), Glu-NH2, Tau, and exogenous L-homoarginine(+) (hoArg(+)). When hoArg(+) was infused (leading to a C-pl = 5.9 mmol/l), C-ti of hoArg(+) was similar throughout the kidney (13-22 nmoo/kg wet wt). In the presence of hoArg(+), C-cH2O/C-pH2O of Arg(+) rose 13-fold. We conclude that 1) AA contribute 20% to cytosolic osmolality in renal cortex, 2) total [AA] decreases from cortex to papilla, 3) cellular uptake of Tau and anionic AA must be rheogenic, whereas cationic AA (except for Arg(+) in cortex) are passively distributed, and 4) AA do not seem to contribute quantitatively to short-term medullary osmotic adaptation during diuresis.