Studies of glutamine uptake across human skeletal sarcolemma.
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 (KpNPPase) and 5'-nucleotidase) was increased approximately 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 muM glutamine in the presence of 0.1 M NaCl = 7 (+/- 1.7) x 10(-3) pmol.mg(-1) protein.s(-1) compared to 1.5 (+/- 0.3) x 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.
Ahmed
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Department of Anatomy and Physiology, University of Dundee, Dundee DD1 4HN, Scotland.