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Regulation of the rat intestinal phosphate transporter NaPi‐2b by dietary phosphate

Elevated serum phosphate (Pi) remains a clinical challenge in patients with chronic kidney diseases. Pi homeostasis is determined by intestinal absorption and renal excretion. Intestinal Pi absorption is mediated by sodium‐dependent Pi uptake across the apical membrane of enterocytes by the NaPi‐2b transporter. Studies in mice have shown expression of NaPi‐2b mainly in the ileum. In contrast, in rats absorption of Pi occurs in the duodenum and jejunum, but not in ileum, a pattern similar to humans. Protein studies in rats have been not possible because of a lack of suitable antibodies. We report here the use of a specific antibody used successfully in rats for the study of the regulation of NaPi‐2b. We found that NaPi‐2b transporter mRNA and protein is mainly expressed in jejunum, with lower levels in duodenum and negligible amounts in ileum. NaPi‐2b expression as well as Na‐dependent Pi uptake was increased in rats adapted to a chronic low Pi diet (0.1% Pi) both in duodenum and jejunum. All these results were confirmed by immunofluorescence microscopy in intestinal sections. In addition, we studied mRNA expression of the type III NaPi transporters: Pit‐1 is highly expressed in all three segments and Pit‐1 mRNA is regulated by dietary Pi. In conclusion, regulation of intestinal Pi transport and NaPi‐2b by dietary Pi in rats is concentrated at duodenum and jejunum sections. This research was supported by NIH and AHA.