Cloning and characterization of a type III Na-dependent phosphate cotransporter from mouse intestine.
Intestinal and renal absorption of inorganic phosphate (P(i)) is critical for phosphate homeostasis in mammals. We have isolated a cDNA that encodes a type III Na-dependent phosphate cotransporter from mouse small intestine (mPit-2). The nucleotide sequence of mPit-2 predicts a protein of 653 amino acids with at least 10 putative transmembrane domains. Kinetic studies, carried out in Xenopus oocytes, showed that mPit-2 cRNA induces significant Na-dependent P(i) uptake with an apparent Michaelis constant (K(m)) for phosphate of 38 microM. The transport of phosphate by mPit-2 is inhibited at high pH. Northern blot analysis demonstrated the presence of mPit-2 mRNA in various tissues, including intestine, kidney, heart, liver, brain, testis, and skin. The highest expression of mPit-2 in the intestine was found in the jejunum. In situ hybridization revealed that mPit-2 mRNA is expressed throughout the vertical crypt-villus axis of the intestinal epithelium. The presence of mPit-2 in the mouse intestine and its unique transport characteristics suggest that multiple Na-dependent cotransporters may contribute to phosphate absorption in the mammalian small intestine.
Bai
L
L
Departments of Pediatrics and Physiology, Steele Memorial Children's Research Center, University of Arizona Health Sciences Center, Tucson, Arizona 85724, USA.
Collins
J F
JF
Ghishan
F K
FK
D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D002478:Cells, Cultured; D003001:Cloning, Molecular; D015870:Gene Expression; D007408:Intestinal Absorption / Q000235:genetics; D007421:Intestine, Small / Q000378:metabolism*; D017136:Ion Transport / Q000235:genetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008845:Microinjections; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D009928:Organ Specificity / Q000235:genetics; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D014982:Xenopus laevis
D002352:Carrier Proteins; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters