A Sodium-independent Mechanism for L-Arginine Uptake by Rat Renal Brush Border Membrane Vesicles

Abstract

L-arginine accumulation in renal cortex slices or in brush border membrane vesicles differs from that of neutral amino acids and sugars, since it can occur despite a lack of sodium in the incubation medium. L-arginine uptake was measured under different conditions in order to determine the relative importance of the Na ⁺ independent component of this transport. In contrast to D-glucose, which was accumulated into the vesicles only in the presence of a NaCl gradient, the accumulation of L-arginine was induced by NaCl, LiCl, KCl, or choline CI gradients. The uptakes of L-arginine and D-glucose were proportional to the membrane potential (inside < 0), but the presence of Na⁺ was not required for the L-arginine uptake. No difference was observed in K_j values of the L-arginine uptake measured with low or high concentration of salt (Li⁺ or Na⁺). J_max were also in the same range of magnitude. An influx of D-glucose or L-alanine (Na⁺ cotransported molecules) induced an increase of the sodium content in vesicles equilibrated with 22Na; the L-arginine uptake did not induce it.

These different results suggest that the electrical potential and not the chemical gradient was the major driving force for the L-arginine uptake.

Key Words:

• rat kidney
• brush border
• plasma membrane
• L-arginine uptake
• Na⁺ dependence
• vesicles.