Cellular mechanisms of acute and chronic adaptation of rat renal P(i) transporter to alterations in dietary P(i).
Recently, the cDNA for a Na-P(i) cotransport system of rat kidney cortex (NaPi-2) has been identified by expression cloning. Using polyclonal antibodies raised against this renal Na-P(i) cotransport system, and using the polymerase chain reaction after reverse transcription of mRNA in microdissected nephron segments, we recently demonstrated that NaPi-2-related mRNA and protein is expressed in the brush-border membranes (BBM) of the proximal tubules of rat kidney. The purpose of the present study was to study the cellular mechanisms involved in adaptation of rat renal Na-P(i) cotransporter to acute and chronic alterations in dietary P(i). Compared with rats fed chronically (7 days) a high-P(i) diet (1.2%), in rats fed chronically a low-P(i) (0.1%) diet the 3.4-fold increase in BBM Na-P(i) cotransport rate (chronic upregulation) was associated with a 2.2-fold increase in renal cortical NaPi-2 mRNA and a 4.9-fold increase in BBM NaPi-2 protein abundances. In contrast, compared with rats fed chronically (7 day) a high-P(i) diet, in rats fed acutely (2 h) a low-P(i) diet the 1.5-fold increase in Na-P(i) cotransport rate (acute upregulation) was associated with a 1.8-fold increase in NaPi-2 protein but no change in NaPi-2 mRNA abundance. Similarly, compared with rats fed chronically a low-P(i) diet, in rats fed acutely (2 h) a high-P(i) diet the 1.9-fold decrease in Na-P(i) cotransport rate (acute downregulation) was associated with a 3.8-fold decrease in NaPi-2 protein but no change in NaPi-2 mRNA abundance.(ABSTRACT TRUNCATED AT 250 WORDS)
Levi
M
M
Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas.
Lötscher
M
M
Sorribas
V
V
Custer
M
M
Arar
M
M
Kaissling
B
B
Murer
H
H
Biber
J
J
D000064:Acclimatization; D000818:Animals; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D016650:Fluorescein-5-isothiocyanate; D015870:Gene Expression; D007150:Immunohistochemistry; D007672:Kidney Cortex / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008297:Male; D008871:Microvilli / Q000378:metabolism*; D009399:Nephrons / Q000378:metabolism*; D010710:Phosphates / Q000008:administration & dosage / Q000378:metabolism*; D010761:Phosphorus Radioisotopes; D016226:Phosphorus, Dietary; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D013997:Time Factors
D002352:Carrier Proteins; D010710:Phosphates; D010761:Phosphorus Radioisotopes; D016226:Phosphorus, Dietary; D012333:RNA, Messenger; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D012964:Sodium; D016650:Fluorescein-5-isothiocyanate