AJP - Endocrinology and Metabolism, Vol 241, Issue 3 191-E195, Copyright © 1981 by American Physiological Society
Transport of glucose analogues in rat lung
J. S. Kerr, A. B. Fisher and A. Kleinzeller
Uptake of nonmetabolizable glucose analogues was investigated in isolated
rat lungs ventilated with 5% CO2 in air and perfused with Krebs-Ringer
bicarbonate medium. In some experiments, [5-3H]glucose,
methyl(alpha-D-[U-14C]gluco)pyranoside (alpha-MG),
3-O-methyl-D-[U-14C]glucose (3-O-MG), or various inhibitors were added to
the initial perfusate to determine glucose utilization by the rate of 3H2O
production or to characterize the uptake of glucose analogues.
[1,2-3H]polyethylene glycol (PEG) was used as an indicator of the
extracellular water space and gave a mean value of 0.35 ml/g tissue;
calculated mean intracellular H2O space was 0.48 ml/g tissue. Glucose
utilization was 56.4 +/- 6.6 (mean +/- SE, n = 6) mumol . g dry wt-1 . h-1
and decreased by 61% with 3 mM phlorizin. After 1-2 h perfusion,
intracellular alpha-MG concentration was 1.4-1.9 times the extracellular
concentration. The mean tissue-to-medium ratio (T/M) for alpha-MG decreased
by more than 30% in the presence of glucose (5.0 mM), phlorizin (0.5 mM),
ouabain (0.5 mM), or the absence of external Na+. Intracellular 3-O-MG
concentration did not exceed extracellular concentration during 2 h of
perfusion and the mean T/M did not change with any of the inhibitors
studied. The results indicate that the nonmetabolizable glucose analogue
alpha-MG is accumulated against a concentration gradient by an active
Na+-dependent transport process, whereas 3-O-MG is apparently taken up by a
different mechanism.
