Expression of Na+–glucose cotransporter (SGLT1) in visceral and parietal mesothelium of rabbit pleura

Indirect evidence for a solute-coupled liquid absorption from rabbit pleural space indicated that it should be caused by a Na+/H+–Cl−/HCO3− double exchanger and a Na+–glucose cotransporter [Agostoni, E., Zocchi, L., 1998. Mechanical coupling and liquid exchanges in the pleural space. In: Antony, V.B. (Ed.), Clinics in Chest Medicine: Diseases of the Pleura, vol. 19. Saunders, Philadelphia, pp. 241–260]. In this research we tried to obtain molecular evidence for Na+–glucose cotransporter (SGLT1) in visceral and parietal mesothelium of rabbit pleura. To this end we performed immunoblot assays on total protein extracts of scraped visceral or parietal mesothelium of rabbits. These showed two bands: one at 72 kDa (m.w. of SGLT1), and one at 55 kDa (which should also provide Na+–glucose cotransport). Both bands disappeared in assays in which SGLT1 antibody was preadsorbed with specific antigen. Molecular evidence for Na+/K+ ATPase (α1 subunit) was also provided. Immunoblot assays for SGLT1 on cultured mesothelial cells of rabbit pleura showed a band at 72 kDa, and in some cases also at 55 kDa, irrespectively of treatment with a differentiating agent. Solute-coupled liquid absorption hinders liquid filtration through parietal mesothelium caused by Starling forces, and favours liquid absorption through visceral mesothelium caused by these forces.