Expression of type IINa-P-i cotransporter in alveolar type II cells

Type II Na-P-i cotransporters (type IIa and type IIb) represent apically lo cated Na-P-i cotransporters in epithelia of proximal tubules (type IIa) and small intestine (type IIb). Here we provide evidence that the type IIb (bu t not the type IIa) Na-P-i cotransporter is also expressed in the lung. Wit h the use of immunohistochemistry, location of the type IIb protein was fou nd exclusively in the apical membrane of type II cells of the alveolar epit helium. Such a location of the type IIb cotransporter suggests an involveme nt in the reuptake of phosphate necessary for the synthesis of surfactant. A possible regulation of the abundance of the type IIb cotransporter in the lung was studied after adaptation of mice to a low-P-i diet. After a chron ic adaptation to a low-P-i diet, no changes in the type IIb protein and the type IIb transcript were observed. These results exclude dietary intake of phosphate as a regulatory factor of the type IIb Na-P-i cotransporter in a lveolar type IT cells.