Effects of dietary Pi on the renal Na+-dependent Pi transporter NaPi-2 in thyroparathyroidectomized rats.
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.
Takahashi
F
F
Department of Clinical Nutrition, School of Medicine, Tokushima University, Kuramoto-Cho 3, Tokushima 770, Japan.
Morita
K
K
Katai
K
K
Segawa
H
H
Fujioka
A
A
Kouda
T
T
Tatsumi
S
S
Nii
T
T
Taketani
Y
Y
Haga
H
H
Hisano
S
S
Fukui
Y
Y
Miyamoto
K I
KI
Takeda
E
E
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000096:biosynthesis / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology; D015151:Immunoblotting; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D007672:Kidney Cortex / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D009399:Nephrons / Q000187:drug effects / Q000378:metabolism; D010281:Parathyroid Hormone / Q000378:metabolism / Q000494:pharmacology; D016105:Parathyroidectomy; D010710:Phosphates / Q000008:administration & dosage / Q000494:pharmacology*; D016226:Phosphorus, Dietary / Q000008:administration & dosage / Q000494:pharmacology*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D013965:Thyroidectomy
D002352:Carrier Proteins; D010281:Parathyroid Hormone; D010710:Phosphates; D016226:Phosphorus, Dietary; D012333:RNA, Messenger; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters