Difference in the effect of phloridzin on alveolar fluid absorption in anesthetized rats and in ex vivo rat lungs

We reexamined the effect of phloridzin on alveolar fluid absorption by utilizing ex vivo rat lungs, which are considered to be a useful tool to investigate electrolyte and fluid transport across alveolar epithelium. Alveolar fluid absorption was almost completely reduced by 10(-3) M phloridzin with 10(-4) M amiloride as reported previously. However, we found that phloridzin alone was also able to significantly reduce alveolar fluid absorption. We then examined the effect of phloridzin on lung metabolism and compared the data with those determined in the presence of iodoacetic acid (IAA) and NaCN. Phloridzin reduced alveolar glucose uptake with no decrease in lung AIP content. Both IAA and NaCN decreased lung AIP content significantly. Our data indicate that the effect of phloridzin on alveolar fluid absorption in ex vivo rat lungs is not the secondary effect to the alteration of lung energy metabolism. Therefore our data support the current concept that Na+-glucose cotransport is involved with transalveolar active Na+ transport, which is a separated pathway from amiloride-sensitive Na+ channels.