Studies of glutamine uptake across human skeletal sarcolemma

Abstract

In the human body skeletal muscle is the largest store of glutamine, an important amino-acid in whole body nitrogen balance. Glutamine transport was measured in purified human skeletal muscle sarcolemmal vesicles (HMSV). The activity of sarcolemmal marker enzymes (K +-stimulated nitrophenylphosphatate (K pNPPase) and 5′-nucleotidase) was increased ∼ 14-fold in the sarcolemmal fraction (SF) compared to the crude muscle homogenate (CH). Glutamine transport in HMSV was Na +-dependent (initial rate of 1 μM glutamine in the presence of 0.1 M NaCl = 7 (± 1.7) × 10 −3 pmol.mg −1 protein.s −1 compared to 1.5 (± 0.3) × 10 −3 pmol mg −1 protein.s −1 in the presence of 0.1 M Choline Cl). The rate of glutamine uptake into HMSV was increased in the presence of an inside negative membrane potential.