title: Internalization of renal type IIc Na-Pi cotransporter in response to a high-phosphate diet.
abstract: Dietary phosphate levels regulate the renal brush-border type IIa Na-Pi cotransporter. Another Na-Pi cotransporter, type IIc, colocalizes with type IIa Na-Pi cotransporter in the apical membrane of renal proximal tubular cells. The goal of the present study was to determine whether dietary phosphate levels also rapidly regulate the type IIc Na-Pi cotransporter. Type IIa and type IIc transporter protein levels were increased in rats chronically fed a low-Pi diet compared with those fed a normal-Pi diet. Two hours after beginning a high-Pi diet, type IIa transporter levels were decreased, whereas type IIc protein levels remained unchanged. Western blot analysis of brush-border membrane prepared 4 h after beginning a high-Pi diet showed a significant reduction in type IIc transporter protein levels, and immunohistochemistry showed translocation of the type IIc-immunoreactive signal from the entire brush border to subapical membrane. Membrane fractionation studies revealed a decrease in apical membrane type IIc protein without changes in total cortical type IIc protein, which is compatible with redistribution of type IIc protein from the apical membrane to the dense membrane fraction. The microtubule-disrupting reagent colchicine prevented this reduction in apical type IIc transporter at the apical membrane but had no effect on type IIa transporter levels. These data suggest that the type IIc Na-Pi cotransporter level is rapidly regulated by rapid adaptation to dietary Pi in a microtubule-dependent manner. Furthermore, the mechanisms of the internalization of the type IIc transporter are distinct from those of the type IIa transporter.
authors.affiliation: Nutritional Science, Dept. of Nutrition, School of Medicine, Tokushima Univ., Kuramoto-Cho 3, Tokushima City 770-8503, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Segawa
authors.forename: Setsuko
authors.initials: S
authors.lastname: Yamanaka
authors.forename: Mikiko
authors.initials: M
authors.lastname: Ito
authors.forename: Masashi
authors.initials: M
authors.lastname: Kuwahata
authors.forename: Masayuki
authors.initials: M
authors.lastname: Shono
authors.forename: Tadashi
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Miyamoto
mesh_terms: D000818:Animals; D004032:Diet; D015536:Down-Regulation / Q000502:physiology; D015151:Immunoblotting; D007150:Immunohistochemistry; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D007672:Kidney Cortex / Q000187:drug effects / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008297:Male; D008566:Membranes / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008870:Microtubules / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D010455:Peptides / Q000276:immunology; D010710:Phosphates / Q000494:pharmacology*; D016226:Phosphorus, Dietary / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters / Q000378:metabolism*
chemical_list: D010455:Peptides; D010710:Phosphates; D016226:Phosphorus, Dietary; C493556:Slc34a1 protein, rat; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters