Regulation of rat Na+/Pi cotransporter-1 gene expression: the roles of glucose and insulin

Li, H.; Ren, Ping; Onwochei, Michael O.; Ruch, Randall J.; Xie, Zijian

doi:10.1152/ajpendo.1996.271.6.e1021

Cited by 18 publications

(26 citation statements)

References 20 publications

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“…Hence, these data suggest that PiT-1 and PiT-2 play an important role in basolateral P i uptake in rat liver. Although it has been suggested that NaPi-I serves to supply the great demand of P i in the liver required for the high level of intracellular glucose metabolism (26), the physiological role of NaPi-I as sodium-phosphate cotransporter remains unclear (42).…”

Section: Discussionmentioning

confidence: 99%

Identification and localization of sodium-phosphate cotransporters in hepatocytes and cholangiocytes of rat liver

Frei¹,

Gao²,

Hagenbuch³

et al. 2005

American Journal of Physiology-Gastrointestinal and Liver Physi

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. Identification and localization of sodium/phosphate cotransporters in hepatocytes and cholangiocytes of rat liver. Am J Physiol Gastrointest Liver Physiol 288: G771-G778, 2005. First published November 24, 2004; doi:10.1152/ajpgi.00272.2004.-Hepatocytes and cholangiocytes release ATP into bile, where it is rapidly degraded into adenosine and Pi. In rat, biliary Pi concentration (0.01 mM) is ϳ100-fold and 200-fold lower than in hepatocytes and plasma, respectively, indicating active reabsorption of biliary Pi. We aimed to functionally characterize canalicular Pi reabsorption in rat liver and to identify the involved Pi transport system(s). Pi transport was determined in isolated rat canalicular liver plasma membrane (LPM) vesicles using a rapid membrane filtration technique. Identification of putative Pi transporters was performed with RT-PCR from liver mRNA. Phosphate transporter protein expression was confirmed by Western blotting in basolateral and canalicular LPM and by immunofluorescence in intact liver. Transport studies in canalicular LPM vesicles demonstrated sodium-dependent Pi uptake. Initial Pi uptake rates were saturable with increasing Pi concentrations, exhibiting an apparent Km value of ϳ11 M. Pi transport was stimulated by an acidic extravesicular pH and by an intravesicular negative membrane potential. These data are compatible with transport characteristics of sodiumphosphate cotransporters NaPi-IIb, PiT-1, and PiT-2, of which the mRNAs were detected in rat liver. On the protein level, NaPi-IIb was detected at the canalicular membrane of hepatocytes and at the brush-border membrane of cholangiocytes. In contrast, PiT-1 and PiT-2 were detected at the basolateral membrane of hepatocytes. We conclude that NaPi-IIb is most probably involved in the reabsorption of P i from primary hepatic bile and thus might play an important role in the regulation of biliary P i concentration.NaPi; PiT; bile formation; transport BOTH HEPATOCYTES AND CHOLANGIOCYTES constitutively release substantial amounts of ATP into bile (16). Within the bile canalicular lumen ATP is quickly degraded by membranebound ecto-ATPases and ecto-5Ј-nucleotidases into adenosine and P i (34). These degradation pathways result in a biliary ATP concentration of ϳ20 nM (9). Although the degradation product adenosine has been shown to be reabsorbed into hepatocytes by sodium-dependent purine nucleoside transporter-1 (SPNT1) (10, 11), the fate of released intrabiliary P i is not known. However, the biliary concentration of P i remains ϳ14 M under physiological circumstances (29), which is considerably lower than the P i concentrations in hepatocytes (ϳ1 mM) (21) and in rat plasma (2.3 mM) (29). This low physiological P i concentration in bile suggests that, similar to adenosine, biliary P i is also actively reabsorbed into hepatocytes and/or into cholangiocytes. To test this hypothesis, we performed P i transport studies in isolated canalicular rat liver plasma membrane (LPM) vesicles and identified the involved P i transport system by RT-PC...

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Section: Discussionmentioning

confidence: 99%

Identification and localization of sodium-phosphate cotransporters in hepatocytes and cholangiocytes of rat liver

Frei¹,

Gao²,

Hagenbuch³

et al. 2005

American Journal of Physiology-Gastrointestinal and Liver Physi

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“…In addition, the regulation of the type II transporter by dietary P i and PTH was shown to differ between PSTs and PCTs (12,13). In contrast, insulin and glucose can affect the expression of the rat type I transporter (14).…”

Section: Vitamin D Is An Important Regulator Of Phosphate Homeostasismentioning

confidence: 98%

Regulation of Type II Renal Na+-dependent Inorganic Phosphate Transporters by 1,25-Dihydroxyvitamin D3

Taketani

Segawa

Chikamori

et al. 1998

Journal of Biological Chemistry

127

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Vitamin D is an important regulator of phosphate homeostasis. The effects of vitamin D on the expression of renal Na؉ -dependent inorganic phosphate (P i ) transporters (types I and II) were investigated. In vitamin D-deficient rats, the amounts of type II Na ؉ -dependent P i transporter (NaPi-2) protein and mRNA were decreased in the juxtamedullary kidney cortex, but not in the superficial cortex, compared with control rats. The administration of 1,25-dihydroxyvitamin D 3 (1,25-(OH) 2 D 3 ) to vitamin D-deficient rats increased the initial rate of P i uptake as well as the amounts of NaPi-2 mRNA and protein in the juxtamedullary cortex. The transcriptional activity of a luciferase reporter plasmid containing the promoter region of the human type II Na ؉ -dependent P i transporter NaPi-3 gene was increased markedly by 1,25-(OH) 2 D 3 in COS-7 cells expressing the human vitamin D receptor. A deletion and mutation analysis of the NaPi-3 gene promoter identified the vitamin D-responsive element as the sequence 5-GGGGCAGCAAGGGCA-3 nucleotides ؊1977 to ؊1963 relative to the transcription start site. This element bound a heterodimer of the vitamin D receptor and retinoid X receptor, and it enhanced the basal transcriptional activity of the promoter of the herpes simplex virus thymidine kinase gene in an orientation-independent manner. Thus, one mechanism by which vitamin D regulates P i homeostasis is through the modulation of the expression of type II Na ؉ -dependent P i transporter genes in the juxtamedullary kidney cortex.The reabsorption of inorganic phosphate (P i ) in the renal proximal tubule plays a key role in overall P i homeostasis (1, 2).1 regulates P i homeostasis in the bone, intestine, and kidney (2). However, the effect of 1,25-(OH) 2 D 3 on the reabsorption of P i in the kidney remains unclear. Contradictory results showing an increase or decrease in P i excretion in response to 1,25-(OH) 2 D 3 have been reported (2). The results may be due to differences in the mode of action (genomic action versus non-genomic action) of 1,25-(OH) 2 D 3 , and/or to differences in the experimental conditions including the time of exposure, dose of 1,25-(OH) 2 D 3 , and previous status of vitamin D and parathyroid hormone (PTH) (2). A study using a micropuncture technique, in situ microperfusion, isolated perfused tubules, and primary cell cultures revealed an axial heterogeneity in proximal tubular P i transport (2). The extent of Na ϩ -P i co-transport is greater in the proximal convoluted tubules (PCTs) than in the proximal straight tubules (PSTs) (3-8). Kinetic studies have shown that the greater P i transport in the PCT is attributable to a higher V max of Na ϩ -P i co-transport (6 -8). Several Na ϩ -P i co-transporters have been isolated from the kidney cortex of various species (9 -11). They have been classified into two different types on the basis of their predicted amino acid sequences: type I, which includes NaPi-1 (rabbit), NPT-1 (human), Npt-1 (mouse), and RNaPi-1 (rat); and type II, which includes NaPi-2/...

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“…This glucose-dependent increase in rNa-P i 1 mRNA expression was independent of insulin, since it was observed in diabetic rats. In primary cell cultures from rat hepatocytes, high glucose concentrations (10-30 mmol/L) also increased rNa-P i type I mRNA (but not Ram-1 mRNA) expression, but only if insulin (10 nmol/L) was present in the medium (Li et al 1996). Since we have used a DME/F12 ''high glucose'' medium containing 25 mmol/L D-glucose, this might have induced the expression of Na-P i 1 in these primary cell cultures of MTAL cells.…”

Section: Expression Of Na-p I Type I In Mtal Cellsmentioning

confidence: 94%

“…In both rat kidneys and cultured hepatocytes, high glucose concentrations selectively upregulated Na-P i type I expression (Li et al 1996). In rat brain, BNP-1 (a Na-P i cotransporter belonging to the type I Na-P i cotransporter family) may be involved in brain energy metabolism (Ni et al 1995).…”

Section: Hypotheses On Na-p I 1 Activation During Ischemiamentioning

confidence: 99%

Na–P_icotransporter type I activity causes a transient intracellular alkalinization during ATP depletion in rabbit medullary thick ascending limb cells

Jans

Ameloot

Wouters

et al. 2008

Can. J. Physiol. Pharmacol.

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Abstract:The cellular pathophysiology of renal ischemia-reperfusion injury was investigated in primary cell cultures from rabbit medullary thick ascending limb (MTAL). Metabolic inhibition (MI) was achieved with cyanide and 2-deoxyglucose. Sixty minutes of MI caused a profound but reversible decrease in intracellular concentration of ATP ([ATP]i). Intracellular pH (pHi) first decreased after initiation of MI, followed by a transient alkalinization. When [ATP]i reached its lowest value (<1% of control), the cells slowly acidified to reach a stable pHi of 6.92 after 50 min of MI. In the presence of EIPA (10 mmol/L), the pattern of changes in pHi was unchanged and acidification was not increased, indicating that the Na + /H + exchangers were inactive during ATP depletion. When inorganic phosphate (Pi) or Na + was omitted from the apical solutions during MI, the transient alkalinization was no longer observed and the cytosol slowly acidified. Experiments on Na + -dependent alkalinizations revealed the presence of a Na-Pi cotransporter in the apical cell membrane. With indirect immunofluorescence, the Na-Pi cotransporter expressed in these primary cell cultures could be identified as Na-Pi type I. Although the exact physiological role of Na-P i type I still is unresolved, these experiments demonstrate that apical Na-P i type I activity is increased at the onset of ATP depletion in MTAL cells.Key words: MTAL, cell culture, ischemia, metabolic inhibition, intracellular pH, alkalinization, Na-P i cotransporter.Résumé : On a examiné la pathophysiologie cellulaire de la lésion d'ischémie-reperfusion rénale dans des cultures de cellules primaires provenant de la branche ascendante large médullaire (BALM). On a induit une inhibition métabolique (IM) au moyen de cyanure et de 2-désoxyglucose. Après 60 min, l'IM a causé une inhibition profonde mais réversible de la [ATP] i . Après le déclenchement de l'IM, il y a eu une diminution du pH i , suivie d'une alcalinisation transitoire. Lorsque que la [ATP] i a atteint sa valeur minimale (<1 % de la valeur témoin), les cellules se sont acidifiées lentement pour atteindre un pH i stable de 6,92 après 50 min. En présence d'EIPA (10 mmol/L), le profil des modifications du pH i est demeuré inchangé et l'acidification n'a pas augmenté, ce qui indique que les échangeurs Na + /H + ont été inactifs durant la déplétion de l'ATP. En l'absence de Pi ou de Na + dans les solutions apicales durant l'IM, l'alcalinisation transitoire a disparu et le cytosol s'est acidifié lentement. Les expériences sur les alcalinisations dépendantes du Na + ont révélé la présence d'un cotransporteur Na-Pi dans la membrane cellulaire apicale. L'immunofluorescence indirecte a permis d'identifier que le cotransporteur Na-Pi exprimé dans ces cultures de cellules primaires est le Na-Pi de type 1. Le rôle physiologique exact du Na-Pi de type 1 n'est toujours pas connu; toutefois, ces expériences démontrent que l'activité apicale de ce cotransporteur augmente au début de la déplétion de l'ATP dans les cellules de la BALM.

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Regulation of rat Na+/Pi cotransporter-1 gene expression: the roles of glucose and insulin

Cited by 18 publications

References 20 publications

Identification and localization of sodium-phosphate cotransporters in hepatocytes and cholangiocytes of rat liver

Identification and localization of sodium-phosphate cotransporters in hepatocytes and cholangiocytes of rat liver

Regulation of Type II Renal Na+-dependent Inorganic Phosphate Transporters by 1,25-Dihydroxyvitamin D3

Na–P_icotransporter type I activity causes a transient intracellular alkalinization during ATP depletion in rabbit medullary thick ascending limb cells

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Regulation of rat Na+/Pi cotransporter-1 gene expression: the roles of glucose and insulin

Cited by 18 publications

References 20 publications

Identification and localization of sodium-phosphate cotransporters in hepatocytes and cholangiocytes of rat liver

Identification and localization of sodium-phosphate cotransporters in hepatocytes and cholangiocytes of rat liver

Regulation of Type II Renal Na+-dependent Inorganic Phosphate Transporters by 1,25-Dihydroxyvitamin D3

Na–Picotransporter type I activity causes a transient intracellular alkalinization during ATP depletion in rabbit medullary thick ascending limb cells

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Na–P_icotransporter type I activity causes a transient intracellular alkalinization during ATP depletion in rabbit medullary thick ascending limb cells