Regulation of small intestinal Na-Pi type IIb cotransporter by dietary phosphate intake

Dietary restriction of phosphate is a well-known stimulator (acting indirectly via vitamin Ds) of small intestinal apical Na-P-i cotransport. In the present study, we document by Western blots and immunohistochemistry that, in mice, a low-P-i diet given for several days leads (in parallel to a stimulation of Na-P-i cotransport) to an increase of the abundance of the type IIb Na-P-i cotransporter in the brush-border membrane of mouse enterocytes. Similar results were also obtained by an injection of cholecalciferol. The abundance of the type IIb transcript was investigated by Northern blots. These results indicated that the amount of the type IIb transcript was not changed by either low-P-i diet or cholecalciferol. It is concluded that stimulation of intestinal Na-P-i cotransport by low-P-i diet and vitamin D-3 can be explained by an increased amount of type IIb Na-P-i cotransporters in the brush-border membrane and that augmentation of type IIb Na-P-i cotransporters is not related to an increased rate of transcription of the type IIb gene.