Regulation of glutamine production by skeletal muscle cells in culture.

Cells of the L6 rat myogenic line consume glutamine in contrast to skeletal muscle in vivo, which produces glutamine. The basis of glutamine consumption in the cultured cells and the conditions under which net glutamine production occurs were investigated. After treating cultures with cytosine-1-beta-D-arabinofuranoside to eliminate replicating myoblasts remaining after differentiation, the L6 cells continued to consume glutamine from medium containing normal plasma levels (650 microM). Consumption declined when cells were incubated with 325 microM glutamine, and, at 0 microM, net production occurred. In addition to the tendency to consume glutamine, the cells rapidly consumed glutamic acid. When medium glutamic acid was increased from 70 to 150, 500, and 1,000 microM, glutamine production increased. Alterations in levels of NH3, the other substrate for glutamine synthesis, did not have this effect. The L6 cells were found to have glutamine synthetase activity similar to normal rat skeletal muscle but markedly increased glutaminase activity. In spite of the imbalance in synthetic and degradative activities, however, inhibitor studies with L-methionine sulfoximine and 6-diazo-5-oxo-L-norleucine showed that flux through both pathways influenced net glutamine production.