title: Sodium-dependent phosphate uptake in the jejunum is post-transcriptionally regulated in pigs fed a low-phosphorus diet and is independent of dietary calcium concentration.
abstract: In rodents, severe dietary P restriction increases active phosphate absorption by the intestine. However, it remains unknown if moderate dietary P restriction has a similar effect. Weanling pigs (n = 32; body weight 7.4 +/- 0.55 kg) were used in a 2 x 2 factorial design and fed dietary available P (aP) concentrations of 0.23 or 0.40% and Ca concentrations of 0.58 or 1.00% for 14 d. Diets were formulated on an aP basis instead of a total P basis, because pigs are unable to absorb phytate-P present in corn and soybean meal. Jejunal segments were mounted in modified Ussing chambers for determination of Na(+)-dependent nutrient transport. Intestinal mucosal scrapings were taken for RNA isolation and brush border membrane (BBM) vesicle isolation. Na(+)-dependent phosphate uptake and gene expression of Na-phosphate cotransporter IIb (NaPi-IIb), SGLT-1 (sodium/glucose cotransporter-1), and calbindin D(9k) and protein expression of NaPi-IIb were evaluated. Na(+)-dependent phosphate transport increased (P < 0.05) 46% as dietary aP concentration was decreased. However, increased Na(+)-dependent phosphate uptake was not accompanied by increased NaPi-IIb mRNA expression. Expression of NaPi-IIb protein in the BBM increased (P < 0.01) 84% in pigs fed low-P diets compared with pigs fed adequate-P diets. No dietary Ca effects or aP x Ca interactions were detected for Na-dependent P uptake, mRNA or protein expression of NaPi-IIb, or mRNA expression of calbindin D(9k). These data suggest that restricting dietary aP concentration by only 43% stimulates Na(+)-dependent phosphate uptake and expression of the NaPi-IIb protein in the BBM of the small intestine and through a post-transcriptional mechanism.
authors.affiliation: Department of Animal Sciences, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Kari L
authors.initials: KL
authors.lastname: Saddoris
authors.forename: James C
authors.initials: JC
authors.lastname: Fleet
authors.forename: John S
authors.initials: JS
authors.lastname: Radcliffe
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002136:Calcium, Dietary / Q000008:administration & dosage; D004032:Diet / Q000662:veterinary*; D005260:Female; D007583:Jejunum / Q000378:metabolism*; D008297:Male; D010710:Phosphates / Q000493:pharmacokinetics*; D016226:Phosphorus, Dietary / Q000008:administration & dosage; D012323:RNA Processing, Post-Transcriptional; D012964:Sodium / Q000378:metabolism*; D050614:Sodium-Phosphate Cotransporter Proteins, Type IIb / Q000235:genetics / Q000378:metabolism; D013552:Swine
chemical_list: D002136:Calcium, Dietary; D010710:Phosphates; D016226:Phosphorus, Dietary; D050614:Sodium-Phosphate Cotransporter Proteins, Type IIb; D012964:Sodium; D002118:Calcium