Regulation of phosphate transport by dietary Pi in the small intestine of rats (908.2)

Abstract

Pi homeostasis is tightly controlled by the harmonized action of the intestine, kidney and bone. To date, three Na‐dependent Pi transporters have been found in the small intestine: NaPi2b, Pit‐1 and Pit‐2, but the coordinated modulation of all three by dietary Pi is unclear.Male Wistar rats were fed ad libitum 0.1% vs. 1.2% Pi diets, for either 1, 5 or 10 days. Brush border membrane vesicles (BBMV) and RNA were obtained from duodenum (D), jejunum (J) and ileum (I).0.1% Pi diet increased Na‐dependent Pi transport in D and J BBMV at 1, 5 and 10 days, as well as the expression of NaPi2b, but only in J for Pit‐2. Pit‐1 expression was increased only at 10 days in D and J. In the I, Pi transport was very modest and adaptation to 0.1% Pi diet was not observed, however, NaPi2b and Pit‐2 expressions were increased at all three times. The changes in NaPi2b and Pit‐1 protein expressions were confirmed by immunohistochemistry, but the changes in Pit‐2 were not noticeable.Pi transport was always higher at pH 6.0 than 8.5 but inhibited by phosphonoformic acid. This suggests the existence of a novel Na‐dependent transporter, different from NaPi2b, Pit‐1 and Pit‐2, and regulated within 24 h by dietary Pi.