Characterization of the Chicken Small Intestine Type IIb Sodium Phosphate Cotransporter

Intestinal absorption and renal resorption play a critical role in overall phosphorus homeostasis in chickens. Using RNase-ligase-mediated rapid amplification of cDNA ends PCR, we obtained a cDNA from the broiler small intestine that encodes a type IIb Na-dependent phosphate transporter. The cDNA has an open reading frame of 2,022 bp and predicts a 674-amino acid protein with a molecular mass of approximately 74 kDa. Prediction of membrane spanning domains based on the hydrophilic and hydrophobic properties of the amino acids suggests 8 transmembrane domains, with both the NH(2) and COOH termini being intracellular. The Na-inorganic phosphate (Pi) IIb cotransporter has relative high homology with other type II Na-Pi cotransporters but low homology with the type I or type III Na-Pi cotransporters. Northern blot analysis demonstrated the presence of a single mRNA transcript present predominantly in the small intestine, with the highest expression in the duodenum, followed by the jejunum and ileum. In situ hybridization indicated that the Na-Pi cotransporter mRNA is expressed throughout the vertical cryptvillus axis of the small intestine. Reduction of P in the diet of chicks from hatch to 4 d of age resulted in a significant induction of Na-Pi cotransporter mRNA expression in the small intestine. Further study is needed to elucidate its physiological role in intestinal phosphate absorption in chickens.