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Regulation of glutamine synthetase and glutaminase activities in cultured skeletal muscle cells

✍ Scribed by Robert J. Smith; Sandra Larson; Susan E. Stred; Roberta P. Durschlag

Publisher
John Wiley and Sons
Year
1984
Tongue
English
Weight
924 KB
Volume
120
Category
Article
ISSN
0021-9541

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✦ Synopsis

Abstract

Glutamine is synthesized in skeletal muscle, released to the circulation, and transported to other tissues, where it may provide important substrate for gluconeogenesis, ammoniagenesis, and energy‐yielding pathways. With the ultimate goal of delineating the factors that control glutamine production and release by skeletal muscle, we have studied the regulation of two key enzymes, glutamine synthetase and glutaminase, in the L6 line of rat skeletal muscle cells grown in monolayer culture. The cultured myotubes were found to have glutamine synthetase and phosphate‐dependent glutaminase activities. Glutamine synthetase activity was increased following incubation (1) in glutamine‐free medium (threefold); (2) in medium containing high glutamic acid concentrations (fourfold); and (3) in medium supplemented with dexamethasone (threefold). In each case the increase in glutamine synthetase activity required several hours to reach a maximum and was prevented by cycloheximide, suggesting that the change occurred through increased enzyme biosynthesis. No substances tested were found to affect glutaminase activity. We conclude that glutamine synthetase in cultured skeletal muscle is responsive to substrate, product, and hormonal regulation.

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