Changes in pulmonary expression of hexokinase and glucose transporter mRNAs in rats adapted to hyperoxia

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Abstract
Impairment of lung aconitase activity, citric acid cycle, and mitochondrial respiration by hyperoxia necessitates the elevation of glycolysis for energy production and of pentose shunt activity for reducing equivalents. The molecular mechanisms that allow increased glucose utilization are unknown. Adult male and female rats were adapted to sublethal hyperoxia, equivalent to 83% oxygen at sea level, or air for 7 days. Lung RNA and protein increased in hyperoxia (197 and 57%, respectively), whereas total DNA was unchanged. In hyperoxia, lung total hexokinase (HK) activity increased threefold, and mRNAs for HK-II and -III were specifically upregulated. HK-I mRNA was unchanged. mRNAs for HK-II and -III gradually increased during the first 72 h in hyperoxia. HK-II mRNA was significantly elevated at 72 h, preceding changes in lung cell populations. Although virtually absent in air, HK-II activity was highly expressed in hyperoxia. Among lung glucose transporters, specific expression of mRNAs for GLUT-4 (insulin dependent) and sodium-glucose cotransporter-1 was decreased, whereas that for GLUT-1 was minimally changed. Adaptation to hyperoxia involves coordinated changes in gene expression for the proteins regulating pulmonary glucose transport.