Differences in sodium and D-glucose transport between hamster and rat lungs

Abstract

The purpose of this study was to characterize phloridzin- and amiloride-sensitive transport across blood-gas barrier of hamster and rat lungs. Air spaces of isolated perfused lungs were instilled with a solution containing 22Na or L-[3H]glucose, D-[14C]glucose, and fluorescein isothiocyanate-labeled dextran. Apparent permeability-surface area products (PS) were calculated. Phloridzin (Na(+)-dependent D-glucose transport inhibitor) had no effect on D-glucose or sodium transport out of air spaces in hamster lungs. In contrast, in rat lungs, phloridzin decreased PS for D-glucose by 89% and that for Na by 28%. Trapping of 14CO2 in vascular samples was measured to estimate metabolism. Unlabeled air space D-glucose increased appearance of perfused D-[14C]glucose in air spaces of rat lungs. We conclude that Na(+)-dependent D-glucose transport is important for D-glucose uptake in rat lungs but not in hamster lungs. In hamster lungs, amiloride (Na+ transport inhibitor) also decreased PS for sodium, but drugs known to stimulate sodium transport in rat lungs had no effect. Thus, species differences in active transport processes exist in the distal air spaces of mammalian lungs.

Ventilator-associated Lung Injury Decreases Lung Ability to Clear Edema in Rats

“…Although we reason that the Ṽ Ṽ Ṽ lung clearance-Na,K-ATPase function association is probably a cause-effect relationship (i.e., high VT ventilation downregulates alveolar epithelial Na,K-ATPase, which decreases vectorial Na ϩ flux and thus lung ability to clear edema), the previous and our present studies do not unequivocally prove it. Also, it is possible that other systems that we did not study in the present report may affect the resolution of edema clearance such as Na ϩ /H ϩ exchanger, Na ϩ -HCO 3 Ϫ , Na ϩ /glucose cotransporters, sodium channels, or aquaporins (8,(24)(25)(26)(27).…”

Mechanisms of liquid flux across pulmonary alveolar epithelial cell monolayers

“…Previous studies have reported that ouabain inhibited Na + flux in AT2 cells in culture (20) as well as active Na + transport in normal isolated rat lungs (15). Although other mechanisms such as the Na+/H + antiport or Na+/HCO3-and Na+/glucose cotransporters could contribute to Na + flux and thus liquid flux in our model, their roles in lung epithelial Na ÷ transport appear to be less important (10,32). The definition of specific transport mechanisms responsible for our observations was beyond the scope of this report.…”