Regulation of glucose transport and GLUT1 glucose transporter expression by O₂ in muscle cells in culture

The effect of varying cellular oxygenation on L6 muscle cell 2-deoxy-D- glucose transport, glucose utilization, lactate production, and expression of GLUT1 and GLUT4 transport proteins was investigated. Incubation of L6 myotubes in 3% O₂ (mimicking a state of hypoxia) elevated glucose uptake by 6.5-fold over 48 h relative to cells incubated in 21% O₂ (normoxia). Incubation of L6 cells in hyperoxic conditions (50% O₂) significantly depressed glucose uptake by 0.4-fold. These effects were fully reversible. Incubation in 3% O₂ also caused lactate accumulation and enhanced glucose consumption from the medium. Hypoxia elevated 2-deoxy-D-glucose transport even when the concentration of glucose in the medium was kept constant, suggesting that glucose deprivation alone was not responsible for increased cellular glucose uptake. Incubation in 3% O₂ also elevated 3-O-methylglucose uptake but not amino acid uptake. Cycloheximide prevented the hypoxia-induced increase in glucose uptake, indicating that de novo synthesis of glucose transport-related proteins was the major means by which cells increased glucose uptake. The content of GLUT1 glucose transporter was significantly elevated in total membranes of cells incubated in 3% O₂ and depressed in membranes from cells incubated in hyperoxic conditions, whereas GLUT4 expression was not affected. These results indicate that hypoxia induces an adaptive response of increasing cellular glucose uptake through elevated expression of GLUT1 in an attempt to maintain supply of glucose for utilization by nonoxidative pathways.