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 (Cti, mmol/kg wet wt), in plasma (Cpl), and in urine. In all regions, Cti 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 (CcH2O, mmol/kgH2O) were between 12.4 (Tau) and 0.09 (Orn+), representing cell water-to-plasma water ratios (CcH2O/CpH2O) 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 Cpl = 5.9 mmol/l), Cti of hoArg+ was similar throughout the kidney (13-22 mmol/kg wet wt). In the presence of hoArg+, CcH2O/CpH2O 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.