Aim: 

Functional evidence of Na⁺-glucose cotransport in rat lung has been provided. By autoradiography [³H]phloridzin binding has been found confined to alveolar type II cells in mouse and rabbit lungs.

Methods: 

In this research we checked by immunofluorescence whether Na⁺-glucose cotransporter (SGLT1) is also expressed in alveolar type I cells. To prevent artifacts two primary antibodies and different histological preparations were used. Lungs of anesthetized rats and lambs were fixed by paraformaldehyde, perfused in pulmonary artery, or instilled into a bronchus, respectively. Tissue blocks embedded in paraffin or frozen were then sectioned. Specific anti-SGLT1 antibodies for rat recognizing amino acid sequence 402-420, and 546-596 were used in both species; bound primary antibody was detected by secondary antibody conjugated to fluorescein isothiocianate or Texas red, respectively.

Results and conclusions: 

In rats alveolar type I cells were identified by fluorescein labeled Erythrina cristagalli lectin. Sections were examined by confocal laser-scanning microscope. Both in rats and lambs most alveolar surface was stained by either anti-SGLT1 antibody; no labeling occurred in negative control sections. Hence, SGLT1 is also expressed in alveolar type I cells. This is functionally relevant because type I cells provide 95-97% of alveolar surface, and SGLT1, besides contributing to lung liquid removal under some circumstances, keeps low glucose concentration in lining liquid, which is useful to prevent lung infection.