Fig. 4.

Characterization of sugar transport activity of Past-A. A, COS-7 cells were transfected with blank vector (Vec), Past-A (Past), or rat GLUT4 cDNA. Sixty-four hours after transfection, transfected cells were incubated with one of radiolabeled sugars and solubilized as described in Materials and Methods. Results are averages of four individual experiments, with SEM indicated by error bars. B, Western blot of the membrane fractions. Transporter proteins Past-A and GLUT4 were detected with each antiserum. The positions of standard molecular masses (in kilodaltons) are indicated at left.C, Inhibition of glucose uptake of COS-7 transfected with Past-A cDNA by the protonophore CCCP. Glucose uptake data are expressed as fold stimulation relative to the extent of uptake observed with COS-7 transfected with blank vector not exposed to CCCP. Results are averages of four individual experiments, with SEM indicated by error bars. D, COS-7 transfected cells with Past-A cDNA were incubated at different pH values for glucose uptake. Glucose uptake data are expressed as fold stimulation relative to the extent of uptake observed with COS-7 transfected with Past-A cDNA at a pH of 7.5. Results are averages of four individual experiments, with SEM indicated by error bars. (▴), pH 6.5; (■), pH 7.0; (●), pH 7.5.