Glutamine transport by human intestinal basolateral membrane vesicle

This study characterizes for the first time, by use of a well-validated technique, glutamine transport across human basolateral membrane vesicles. Glutamine transport represented uptake into an osmotically active intravesicular space without significant metabolism. Glutamine uptake was temperature- and pH-dependent with maximal uptake at pH 7.5, and it was mediated by sodium-dependent and -independent processes. The initial rate of uptake was linear up to 20 s, as depicted by the formula y (nmol/mg protein) = 0.0009X (s) - 0.0011 (r = 0.99). Kinetic analysis of glutamine uptake at concentrations between 0.01 and 0.3 mmol/L at 5 s under sodium and potassium gradients showed a maximal transport capacity (V_max) of 0.39 ± 0.04 and 0.21 ± 0.02 nmol · mg protein^-1 · 5 s^-1 for sodium-dependent and -independent processes, respectively (p < 0.01 ). K_m values were 0.17 ± 0.04 and 0.06 ± 0.2 mmol/L, respectively (p < 0.05). Glutamine uptake under the sodium-gradient condition was electrogenic whereas under the potassium-gradient it was electroneutral. Neutral amino acids inhibited both sodium-dependent and -independent processes. This study confirms and characterizes the presence of carrier-mediated glutamine uptake at the basolateral membranes of human enterocytes.