Role of Na⁺ -glucose cotransport in fluid absorption across alveolar epithelium in isolated rat lungs

To evaluate the role of Na⁺-glucose cotransport in fluid absorption across alveolar epithelial walls in isolated rat lungs, we measured the inhibitory effect of amiloride (a Na⁺ channel blocker) and phlorizin (a Na⁺-glucose cotransport blocker) on the fluid absorption rate in fluid- filled lungs. Amiloride (10^-5 - 10^-4 M) reduced alveolar fluid absorption by 30%. This value was similar to that obtained in the presence of 10^-3 M phlorizin. The coefficient of Na⁺-glucose cotransport was estimated to be 2.5. The strong correlation between Na⁺ escape and fluid absorption (r = 0.907) was not affected by phlorizin. These findings suggest that the impact of Na⁺-glucose cotransport was similar to that of Na⁺ transport alone, and that glucose molecules transported by Na⁺-glucose do not play an important role in alveolar fluid absorption across rat alveolar epithelium.