Effect of GLUT1 glucose transporter overexpression on the stimulation of glucose transport in response to inhibition of oxidative phosphorylation.

Glucose transport is markedly stimulated in response to inhibition of oxidative phosphorylation by cyanide or azide in Clone 9 cells, a rat liver cell line in which only the GLUT1 isoform of glucose transporters is expressed. Here, we examine the possibility that the stimulation of glucose transport by azide is similarly observed in cells exhibiting high basal rates of glucose transport. We stably transfected Clone 9 cells with an expression plasmid containing full-length rat GLUT1 cDNA; nontransfected cells and cells transfected with plasmid alone served as controls. Two clones of cells transfected with the GLUT1-cDNA-containing insert, labeled A and B, respectively, expressed 8- and 20-fold higher levels of GLUT1 mRNA, contained 11- and 23-fold higher levels of GLUT1, and manifested 11- and 17-fold higher rates of glucose transport in the basal state. Upon incubation with 5 mM azide for 2 h, the rate of glucose transport was markedly stimulated in both clones. Moreover, the transient fall in cell ATP content following exposure to azide did not correlate with the magnitude of the glucose transport response. We conclude that in GLUT1-overexpressing Clone 9 cells (i) GLUT1 content and glucose transport parallel cellular GLUT1 mRNA content, suggesting no major translational or posttranslational control of GLUT1 expression and function in the basal state, and (ii) the rate of glucose transport in cells overexpressing GLUT1 is markedly stimulated by exposure to azide. These results indicate that the stimulation of glucose transport in response to inhibition of oxidative phosphorylation is maintained in cells with very high basal rates of glucose transport.