Effects of dietary Pi on the renal Na+-dependent Pi transporter NaPi-2 in thyroparathyroidectomized rats

• Published in: Biochemical journal 1998-07, Vol.333 ( Pt 1) (1), p.175-181
• Main Authors: Takahashi, F, Morita, K, Katai, K, Segawa, H, Fujioka, A, Kouda, T, Tatsumi, S, Nii, T, Taketani, Y, Haga, H, Hisano, S, Fukui, Y, Miyamoto, K I, Takeda, E
• Format: Article
• Language: English
• Subjects: Animals; Biological Transport - drug effects; Carrier Proteins - biosynthesis; Carrier Proteins - metabolism; Endocytosis - physiology; Immunoblotting; Kidney - drug effects; Kidney - metabolism; Kidney - ultrastructure; Kidney Cortex - drug effects; Kidney Cortex - metabolism; Kidney Cortex - ultrastructure; Male; Microvilli - drug effects; Microvilli - metabolism; Nephrons - drug effects; Nephrons - metabolism; Parathyroid Hormone - metabolism; Parathyroid Hormone - pharmacology; Parathyroidectomy; Phosphates - administration & dosage; Phosphates - pharmacology; Phosphorus, Dietary - administration & dosage; Phosphorus, Dietary - pharmacology; Rats; Rats, Sprague-Dawley; RNA, Messenger - biosynthesis; Sodium-Phosphate Cotransporter Proteins; Symporters; Thyroidectomy
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj3330175

Dietary Pi and parathyroid hormone (PTH) are two most important physiological and pathophysiological regulators of Pi re-absorption in the renal proximal tubule. Effects of dietary Pi on Na+/Pi co-transporter NaPi-2 were investigated in thyroparathyroidectomized (TPTX) rats. NaPi-2 protein and mRNA in the kidney cortex of TPTX rats were increased approximately 3.8- and 2.4-fold in amount respectively compared with those in the sham-operated animals. Administration of PTH to the TPTX rats resulted in a decrease in the amount of NaPi-2 protein, but not in the abundance of NaPi-2 mRNA. Deprivation of dietary Pi in the TPTX rats did not affect the amount of NaPi-2 mRNA and protein. In the Pi-deprived TPTX rats, feeding of a high-Pi diet resulted in marked decreases in Pi transport activity and the amount of NaPi-2 protein in the superficial nephrons. Immunohistochemical analysis demonstrated that administration of PTH to TPTX rats resulted in a decrease in NaPi-2 immunoreactivity from both superficial and juxtamedullary nephrons within 4 h. Switching TPTX animals from a low-Pi diet to the high-Pi diet decreased NaPi-2 immunoreactivity from superficial nephrons, but not from juxtamedullary nephrons, within 4 h. These results suggest that dietary Pi could regulate the amount of NaPi-2 protein in the superficial nephrons in a PTH-independent manner.