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Differential regulation of the renal sodium-phosphate cotransporters NaPi-IIa, NaPi-IIc, and PiT-2 in dietary potassium deficiency.

Breusegem SY, Takahashi H, Giral-Arnal H, Wang X, Jiang T, Verlander JW, Wilson P, Miyazaki-Anzai S, Sutherland E, Caldas Y, Blaine JT, Segawa H, Miyamoto K, Barry NP, Levi M - Am. J. Physiol. Renal Physiol. (2009)

Bottom Line: Dietary potassium (K) deficiency is accompanied by phosphaturia and decreased renal brush border membrane (BBM) vesicle sodium (Na)-dependent phosphate (P(i)) transport activity.Using Western blotting, immunofluorescence, and quantitative real-time PCR, we found that, in rats and in mice, K deficiency is associated with a dramatic decrease in the NaPi-IIc protein abundance in proximal tubular BBM and in NaPi-IIc mRNA.In summary, our results demonstrate that decreases in BBM abundance of the phosphate transporter NaPi-IIc and also PiT-2 might contribute to the phosphaturia of dietary K deficiency, and that the three renal BBM phosphate transporters characterized so far can be differentially regulated by dietary perturbations.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Division of Renal Diseases and Hypertension, University of Colorado Denver, Aurora, Colorado, USA. syab2@cam.ac.uk

ABSTRACT
Dietary potassium (K) deficiency is accompanied by phosphaturia and decreased renal brush border membrane (BBM) vesicle sodium (Na)-dependent phosphate (P(i)) transport activity. Our laboratory previously showed that K deficiency in rats leads to increased abundance in the proximal tubule BBM of the apical Na-P(i) cotransporter NaPi-IIa, but that the activity, diffusion, and clustering of NaPi-IIa could be modulated by the altered lipid composition of the K-deficient BBM (Zajicek HK, Wang H, Puttaparthi K, Halaihel N, Markovich D, Shayman J, Beliveau R, Wilson P, Rogers T, Levi M. Kidney Int 60: 694-704, 2001; Inoue M, Digman MA, Cheng M, Breusegem SY, Halaihel N, Sorribas V, Mantulin WW, Gratton E, Barry NP, Levi M. J Biol Chem 279: 49160-49171, 2004). Here we investigated the role of the renal Na-P(i) cotransporters NaPi-IIc and PiT-2 in K deficiency. Using Western blotting, immunofluorescence, and quantitative real-time PCR, we found that, in rats and in mice, K deficiency is associated with a dramatic decrease in the NaPi-IIc protein abundance in proximal tubular BBM and in NaPi-IIc mRNA. In addition, we documented the presence of a third Na-coupled P(i) transporter in the renal BBM, PiT-2, whose abundance is also decreased by dietary K deficiency in rats and in mice. Finally, electron microscopy showed subcellular redistribution of NaPi-IIc in K deficiency: in control rats, NaPi-IIc immunolabel was primarily in BBM microvilli, whereas, in K-deficient rats, NaPi-IIc BBM label was reduced, and immunolabel was prevalent in cytoplasmic vesicles. In summary, our results demonstrate that decreases in BBM abundance of the phosphate transporter NaPi-IIc and also PiT-2 might contribute to the phosphaturia of dietary K deficiency, and that the three renal BBM phosphate transporters characterized so far can be differentially regulated by dietary perturbations.

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Renal BBM Na+-coupled phosphate transporters in dietary potassium (K) deficiency in rats. NaPi-IIa abundance increases, while NaPi-IIc and PiT-2 abundance decreases in K-deficient vs. control rat BBM. NaPi-IIa (A), NaPi-IIc (B), and PiT-2 (C) abundance in 6 control and 6 K-deficient rat BBM samples was determined by Western blotting. The bar graphs show average densitometry values ± SD. The experiment was repeated three times, and a representative Western blot and analysis is shown.
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f2: Renal BBM Na+-coupled phosphate transporters in dietary potassium (K) deficiency in rats. NaPi-IIa abundance increases, while NaPi-IIc and PiT-2 abundance decreases in K-deficient vs. control rat BBM. NaPi-IIa (A), NaPi-IIc (B), and PiT-2 (C) abundance in 6 control and 6 K-deficient rat BBM samples was determined by Western blotting. The bar graphs show average densitometry values ± SD. The experiment was repeated three times, and a representative Western blot and analysis is shown.

Mentions: Total renal cortical BBM was isolated from rats fed either a control diet or a K-deficient diet for 14 days. Cortical BBM Na+-coupled Pi transport activity was decreased by almost 40% in BBM isolated from K-deficient rats compared with control rats (from 800 ± 200 to 480 ± 130 pmol 32P·10 s−1·mg BBM protein−1, P = 0.002). Separation of the BBM proteins by SDS-PAGE followed by Western blotting indicated a significant increase in NaPi-IIa BBM abundance in dietary K deficiency (Fig. 2A), in agreement with our laboratory's earlier studies (32). In contrast, NaPi-IIc BBM abundance in dietary K deficiency was dramatically decreased (Fig. 2B), while BBM PiT-2 abundance was also significantly reduced (Fig. 2C). When total renal cortical membranes were assayed, the observed changes in NaPi-IIa, NaPi-IIc, and PiT-2 paralleled the ones seen in the BBM (Supplemental Fig. S1). (The online version of this article contains supplemental data.)


Differential regulation of the renal sodium-phosphate cotransporters NaPi-IIa, NaPi-IIc, and PiT-2 in dietary potassium deficiency.

Breusegem SY, Takahashi H, Giral-Arnal H, Wang X, Jiang T, Verlander JW, Wilson P, Miyazaki-Anzai S, Sutherland E, Caldas Y, Blaine JT, Segawa H, Miyamoto K, Barry NP, Levi M - Am. J. Physiol. Renal Physiol. (2009)

Renal BBM Na+-coupled phosphate transporters in dietary potassium (K) deficiency in rats. NaPi-IIa abundance increases, while NaPi-IIc and PiT-2 abundance decreases in K-deficient vs. control rat BBM. NaPi-IIa (A), NaPi-IIc (B), and PiT-2 (C) abundance in 6 control and 6 K-deficient rat BBM samples was determined by Western blotting. The bar graphs show average densitometry values ± SD. The experiment was repeated three times, and a representative Western blot and analysis is shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2724260&req=5

f2: Renal BBM Na+-coupled phosphate transporters in dietary potassium (K) deficiency in rats. NaPi-IIa abundance increases, while NaPi-IIc and PiT-2 abundance decreases in K-deficient vs. control rat BBM. NaPi-IIa (A), NaPi-IIc (B), and PiT-2 (C) abundance in 6 control and 6 K-deficient rat BBM samples was determined by Western blotting. The bar graphs show average densitometry values ± SD. The experiment was repeated three times, and a representative Western blot and analysis is shown.
Mentions: Total renal cortical BBM was isolated from rats fed either a control diet or a K-deficient diet for 14 days. Cortical BBM Na+-coupled Pi transport activity was decreased by almost 40% in BBM isolated from K-deficient rats compared with control rats (from 800 ± 200 to 480 ± 130 pmol 32P·10 s−1·mg BBM protein−1, P = 0.002). Separation of the BBM proteins by SDS-PAGE followed by Western blotting indicated a significant increase in NaPi-IIa BBM abundance in dietary K deficiency (Fig. 2A), in agreement with our laboratory's earlier studies (32). In contrast, NaPi-IIc BBM abundance in dietary K deficiency was dramatically decreased (Fig. 2B), while BBM PiT-2 abundance was also significantly reduced (Fig. 2C). When total renal cortical membranes were assayed, the observed changes in NaPi-IIa, NaPi-IIc, and PiT-2 paralleled the ones seen in the BBM (Supplemental Fig. S1). (The online version of this article contains supplemental data.)

Bottom Line: Dietary potassium (K) deficiency is accompanied by phosphaturia and decreased renal brush border membrane (BBM) vesicle sodium (Na)-dependent phosphate (P(i)) transport activity.Using Western blotting, immunofluorescence, and quantitative real-time PCR, we found that, in rats and in mice, K deficiency is associated with a dramatic decrease in the NaPi-IIc protein abundance in proximal tubular BBM and in NaPi-IIc mRNA.In summary, our results demonstrate that decreases in BBM abundance of the phosphate transporter NaPi-IIc and also PiT-2 might contribute to the phosphaturia of dietary K deficiency, and that the three renal BBM phosphate transporters characterized so far can be differentially regulated by dietary perturbations.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Division of Renal Diseases and Hypertension, University of Colorado Denver, Aurora, Colorado, USA. syab2@cam.ac.uk

ABSTRACT
Dietary potassium (K) deficiency is accompanied by phosphaturia and decreased renal brush border membrane (BBM) vesicle sodium (Na)-dependent phosphate (P(i)) transport activity. Our laboratory previously showed that K deficiency in rats leads to increased abundance in the proximal tubule BBM of the apical Na-P(i) cotransporter NaPi-IIa, but that the activity, diffusion, and clustering of NaPi-IIa could be modulated by the altered lipid composition of the K-deficient BBM (Zajicek HK, Wang H, Puttaparthi K, Halaihel N, Markovich D, Shayman J, Beliveau R, Wilson P, Rogers T, Levi M. Kidney Int 60: 694-704, 2001; Inoue M, Digman MA, Cheng M, Breusegem SY, Halaihel N, Sorribas V, Mantulin WW, Gratton E, Barry NP, Levi M. J Biol Chem 279: 49160-49171, 2004). Here we investigated the role of the renal Na-P(i) cotransporters NaPi-IIc and PiT-2 in K deficiency. Using Western blotting, immunofluorescence, and quantitative real-time PCR, we found that, in rats and in mice, K deficiency is associated with a dramatic decrease in the NaPi-IIc protein abundance in proximal tubular BBM and in NaPi-IIc mRNA. In addition, we documented the presence of a third Na-coupled P(i) transporter in the renal BBM, PiT-2, whose abundance is also decreased by dietary K deficiency in rats and in mice. Finally, electron microscopy showed subcellular redistribution of NaPi-IIc in K deficiency: in control rats, NaPi-IIc immunolabel was primarily in BBM microvilli, whereas, in K-deficient rats, NaPi-IIc BBM label was reduced, and immunolabel was prevalent in cytoplasmic vesicles. In summary, our results demonstrate that decreases in BBM abundance of the phosphate transporter NaPi-IIc and also PiT-2 might contribute to the phosphaturia of dietary K deficiency, and that the three renal BBM phosphate transporters characterized so far can be differentially regulated by dietary perturbations.

Show MeSH
Related in: MedlinePlus