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PubMed1978

Combined glucose phosphate isomerase and glucose-6-phosphate dehydrogenase deficiency of erythrocytes.

A patient with combined deficiency of erythrocyte glucose phosphate isomerase (GPI) and glucose-6-phosphate dehydrogenase (G6PD) is presented. The propositus has persistent unconjugated hyperbilirubinemia. One of his two brothers exhibits the same rare enzymatic defect, but without any clinical symptoms. The electrophoretic pattern of GPI showed GPI type 1. There seems to be a correlation between the unconjugated hyperbilirubinemia and the combined enzymopathy in our patient.

Adult↗

PubMed1993

A rapid spectrophotometric estimation of individual phosphates and phosphonates: its application to chromatography of sugar phosphates and their phosphonate analogues.

A compound containing the -PO3H2 group (phosphoric acid, one of its monoesters, or an alkylphosphonic acid) may be rapidly assayed by the decrease it produces in the absorbance at 450 nm of a buffered acidic solution of Fe3+ and N(-3) [corrected]. The method has been used to follow chromatograms of sugar phosphates and their phosphonomethyl analogues.

Chromatography, Ion Exchange↗

PubMed1993

Effect of low-phosphate diet on sodium/phosphate cotransport mRNA and protein content and on oocyte expression of phosphate transport.

Recently, we have isolated a complementary DNA most likely related to rabbit kidney cortex brush border membrane sodium/phosphate (Na/Pi) cotransport activity [NaPi-1 (1)]. To further elucidate the cellular mechanisms involved in dietary 'adaptation' of renal Na/Pi cotransport, we have exposed young rabbits for 2 weeks to either a low phosphate (Pi) diet (LPD) or a high Pi diet (HPD). Initial linear uptake of Na/Pi cotransport in isolated brush border membrane vesicles was increased in rabbits on a LPD compared with those on a HPD. Injection of equal amounts of total mRNA isolated from kidney cortex of LPD or HPD rabbits into Xenopus laevis oocytes resulted in a higher stimulation of Na-dependent oocyte Pi uptake in LPD than HPD preparations. No difference in the content of 'specific' mRNA (NaPi-1 cDNA probe, Northern blots) and of the content of the 'specific' brush border membrane protein (NaPi-1 antipeptide antibody, Western blots) between LPD and HPD preparations was observed. We conclude that 'chronic' dietary Pi deprivation leads to a protein synthesis-dependent alteration of Na/Pi cotransport activity which does not involve a change in the total amount of a protein related to the recently cloned NaPi-1 protein.

Animals↗

PubMed1996

Renal expression of Na+-phosphate cotransporter mRNA and protein: effect of the Gy mutation and low phosphate diet.

The X-linked Gy mutation is closely linked, but not allelic, to Hyp and is characterized by rickets, hypophosphatemia, decreased renal tubular maximum for phosphate (Pi) reabsorption (TmP) and a specific reduction in renal brush-border membrane (BBM) Na+-Pi cotransport. Gy mice, like their normal littermates, respond to a low-Pi diet with an increase in BBM Na+-Pi cotransport, but fail to show an adaptive increase in Tmp. Using an antibody raised against the NH2 terminal peptide of the rat renal-specific Na+-Pi cotransporter (NaPi-2) and a NaPi-2 cDNA probe, we examined the effect of the Gy mutation and low-Pi diet (0.03% Pi) on NaPi-2 protein and mRNA abundance. The reduction in BBM Na+-Pi cotransport in Gy mice (51 +/- 5% of normal, P < 0.05) was associated with a decrease in NaPi-2 protein (46 +/- 12% of normal, P < 0.05) and mRNA abundance (76 +/- 5%, P < 0.05). The low-Pi diet elicited a two- to three-fold increase in Na+-Pi cotransport in both normal and Gy mice that was accompanied by a large increase in NaPi-2 protein (10.2-fold in normal and 16.9-fold in Gy mice) and a modest increase in NaPi-2 mRNA (1.3-fold in both mouse strains, P < 0.05). The present data demonstrate that (1) the renal defect in BBM Pi transport in Gy mice can be ascribed to a deficit in NaPi-2 protein and mRNA abundance, (2) both normal and Gy mice respond to low Pi with an adaptive increase in NaPi-2 protein that exceeds the increase in Na+-Pi cotransport activity and NaPi-2 mRNA, (3) the adaptive increase in NaPi-2 protein and mRNA are not sufficient for the overall increase in TmP following Pi restriction.

Animals↗

PubMedDate not supplied

Phosphate depletion with phosphate binder arrests the development of nephropathy in spontaneously hypertensive rats with non-insulin-dependent diabetes mellitus fed a high-protein diet.

The protective effect of phosphate binder (PB) on nephropathy was examined in spontaneously hypertensive rats with non-insulin-dependent diabetes mellitus (NIDDM) fed a high-protein diet. The rats were treated with vehicle or streptozocin neonatally. After 14 weeks, all rats were fed a high-protein diet (50% protein content), and in half of the diabetic rats the diets were supplemented with PB. At 24 weeks, the urinary excretion rate of albumin and kidney weight increased in diabetic rats, but decreased or tended to decrease in diabetic rats treated with PB. The elevation of urinary excretion rate of N-acetyl-beta-D-glucosaminidase, probably due to protein load, was also abolished with PB.

Aluminum Hydroxide↗

PubMed1984

Ureaplasma urealyticum-induced crystallization of magnesium ammonium phosphate and calcium phosphates in synthetic urine.

Crystallization of struvite and calcium phosphates was studied in vitro as encrustations on glass rods immersed in synthetic urine, to evaluate the crystallization capacity of Ureaplasma urealyticum and compare it with that of known urease and non-urease-producing bacteria. Inoculation of the synthetic urine with Ureaplasma urealyticum resulted in alkalinization of the synthetic urine and crystallization of struvite and brushite. Inoculation with Proteus mirabilis caused a faster and more pronounced alkalinization as well as crystallization of struvite and apatite. The alkalinization and crystallization caused by Ureaplasma urealyticum and Proteus mirabilis was completely prevented by acetohydroxamic acid, a potent urease inhibitor, linking the crystallization to the urease activity of the microorganisms. When the synthetic urine was inoculated with urease-negative Escherichia coli no alkalinization and no crystallization were seen.

Calcium Phosphates↗

PubMed1998

Mechanism of inorganic phosphate interaction with phosphate binding protein from Escherichia coli.

The mechanism of Pi interaction with phosphate binding protein of Escherichia coli has been investigated using the A197C mutant protein labeled with a coumarin fluorophore (MDCC-PBP), which gives a fluorescence change on binding Pi. A pure preparation of MDCC-PBP was obtained, in which the only significant inhomogeneity is the presence of equal amounts of two diastereoisomers due to the chiral center formed on reaction of the cysteine with the maleimide. These diastereoisomers could not be separated, but Pi binding data suggest that they differ in affinity and fluorescence change. When Pi binds to MDCC-PBP, the fluorescence quantum yield increases 8-fold and the fluorescence intensity at 465 nm increases 13-fold. The kinetics of Pi binding show saturation of the rate at high Pi concentrations, and this together with other information suggests a two-step mechanism with the fluorescence change after binding, concomitant with a conformational change of the protein that closes the cleft containing the Pi binding site. Cleft closure has a rate constant of 317 s-1 (pH 7.0, 5 degrees C), and opening has a rate constant of 4.5 s-1. The fluorescence increase is likely to arise from a change in the hydrophobic environment during this closure as the steady state fluorescence emission (lambdamax and intensity) on Pi binding is mimicked by the addition of ethanol to aqueous solutions of an MDCC-thiol adduct. Fluorescence lifetimes in the absence and presence of Pi were 0.3 and 2.4 ns, respectively, consistent with the change in quantum yield. The rotational correlation time of the coumarin increases only 2-fold from 15 to 26 ns on binding Pi as measured by time-resolved polarization, consistent with the main rotation being determined by the protein even in the open conformation, but with greater local motion. Circular dichroism of the coumarin induced by the protein is weak in the absence of Pi and increases strongly upon saturation by Pi. These data are also consistent with an open to closed conformational model.

Binding Sites↗

PubMed1999

gamma-L-glutamyl-L-DOPA inhibits Na(+)-phosphate cotransport across renal brush border membranes and increases renal excretion of phosphate.

BACKGROUND: For treatment of phosphate (Pi) overload in various pathophysiological states, an agent that selectively increases renal Pi excretion would be of major value. Previously, we have shown that dopamine (DA) inhibits Na(+)-Pi cotransport in renal epithelia. However, the administration of DA or its immediate precursor L-DOPA increases DA in multiple tissues. Synthetic dipeptide gamma-L-glutamyl-L-DOPA (gludopa) can serve as an inactive precursor (pro-pro-drug) of DA. This study tested the hypothesis that, because of the unique colocalization of gamma-glutamyltransferase (gamma-GT), aromatic amino acid decarboxylase, Na(+)-Pi cotransporter, and Na(+)-L-DOPA cotransporter in brush border membrane (BBM) of proximal tubular cells, gludopa may elicit phosphaturia by action of DA generated within the kidney. METHODS: Thyroparathyrectomized rats were given placebo, or gludopa, or gludopa + gamma-GT inhibitor acivicin. Urinary excretion of Pi, Ca2+, Na+, K+, DA, cAMP, and cGMP was determined, and Na(+)-Pi cotransport was measured in BBM prepared from kidneys of rats at the end of the experiment. RESULTS: The administration of gludopa resulted in: (a) an inhibition of Na(+)-Pi cotransport, but not cotransport of Na(+)-proline and Na(+)-alanine in BBM; (b) an increase (+300%) of fractional excretion (FE) of Pi and a drop (-35%) of plasma Pi, whereas the plasma levels and FEs of Ca2+, Na+, and K+ were unchanged; (c) an increase in urinary excretion of cAMP. but not cGMP; (d) a 1000-fold increase of urinary excretion of DA, without a change in excretion of norepinephrine; and (e) an incubation of gludopa with BBM in vitro, which caused a release of L-DOPA, and the in vivo administration of acivicin, which blocked actions of gludopa to inhibit Na(+)-Pi cotransport and to increase urinary excretions of Pi and DA. CONCLUSIONS: We conclude that colocalization of enzymes of biotransformation, BBM transporters, and the autocrine/paracrine DA system in cells of proximal tubules constitutes a cellular basis for the potent and specific phosphaturic action of gludopa.

Alanine↗

PubMed2000

Natural and azido fatty acids inhibit phosphate transport and activate fatty acid anion uniport mediated by the mitochondrial phosphate carrier.

The electroneutral P(i) uptake via the phosphate carrier (PIC) in rat liver and heart mitochondria is inhibited by fatty acids (FAs), by 12-(4-azido-2-nitrophenylamino)dodecanoic acid (AzDA) and heptylbenzoic acid ( approximately 1 microm doses) and by lauric, palmitic, or 12-azidododecanoic acids ( approximately 0.1 mm doses). In turn, reconstituted E. coli-expressed yeast PIC mediated anionic FA uniport with a similar pattern leading to FA cycling and H(+) uniport. The kinetics of P(i)/P(i) exchange on recombinant PIC in the presence of AzDA better corresponded to a competitive inhibition mechanism. Methanephosphonate was identified as a new PIC substrate. Decanephosphonate, butanephosphonate, 4-nitrophenylphosphate, and other P(i) analogs were not translocated and did not inhibit P(i) transport. However, methylenediphosphonate and iminodi(methylenephosphonate) inhibited both electroneutral P(i) uptake and FA cycling via PIC. AzDA analog 16-(4-azido-2-nitrophenylamino)-[(3)H(4)]-hexadecanoic acid ((3)H-AzHA) bound upon photoactivation to several mitochondrial proteins, including the 30- and 34-kDa bands. The latter was ascribed to PIC due to its specific elution pattern on Blue Sepharose and Affi-Gel. (3)H-AzHA photolabeling of recombinant PIC was prevented by methanephosphonate and diphosphonates and after premodification with 4-azido-2-nitrophenylphosphate. Hence, the demonstrated PIC interaction with monovalent long-chain FA anions, but with divalent phosphonates of short chain only, indicates a pattern distinct from that valid for the mitochondrial uncoupling protein-1.

Affinity Labels↗

PubMed2003

Dual regulation of proton- and sodium-coupled phosphate transport systems in the Yarrowia lipolytica yeast by extracellular phosphate and pH.

In this study we used a newly isolated osmo-, salt-, and alkali-tolerant Yarrowia lipolytica yeast strain, with a unique capacity to grow over a wide pH range (3.5-10.5). A procedure was elaborated to follow phosphate accumulation by Y. lipolytica cells grown at different pH values. In this paper we demonstrate that Pi-starved Y. lipolytica cells are endowed by derepressible high-affinity, high-capacity H(+)- and Na(+)-driven Pi uptake systems and that activities of these transport systems are under the dual control by the prevailing extracellular Pi concentrations and pH values.

Biological Transport↗

PubMed1997

Acute regulation by dietary phosphate of the sodium-dependent phosphate transporter (NaP(i)-2) in rat kidney.

Alteration of the dietary intake of phosphate (P(i)) leads to rapid changes in renal P(i) transport activity. The present study, examined the underlying cellular mechanisms of the rapid regulation, with special reference to renal P(i) cotransporter. Rats were fed either a low-P(i) (0.02%) diet (CLP rats), the low-P(i) diet followed by a high-P(i) (1.2%) diet (AHP rats), or a normal (0.6%) diet (control rats). Na(+)-dependent P(i) transport activity in the brush border membrane was significantly increased in CLP rats compared with control rats, and this activity decreased rapidly within 2 h after the change of diet in AHP rats. Kinetic analysis of P(i) transport in the AHP rats indicated that the reduction was accompanied by a decrease in the apparent Vmax for Na(+)-dependent P(i) uptake. Northern blot analysis showed no difference in the abundance of NaP(i)-2 mRNA of the kidney between AHP and CLP rats. In contrast, Western blot analysis of renal brush border membrane proteins of AHP rats indicated a significant decrease in the abundance of NaP(i)-2 protein as compared with CLP rats. Immunoreactive signals for NaP(i)-2 were detected in lysosomal fractions of AHP and CLP rats. Immunohistochemical analysis showed that, NaP(i)-2 immunoreactivity in AHP rats was largely reduced in the apical membrane of the proximal tubular epithelial cells. Neither cycloheximide nor actinomycin D affected high-P(i)-induced reduction of NaP(i)-2 protein in the brush border membrane of AHP rats, indicating that de novo protein synthesis of an unidentified regulator protein was not involved in the mechanism of this reduction. In contrast, treatment with colchicine, which disrupts microtubulers, abolished the effect of high-P(i) diet on NaP(i)-2 expression. These results suggested that rapid endocytotic internalization of NaP(i)-2 may occur specifically in the brush border membrane following an acute increase in dietary P(i) intake.

Animals↗

PubMed2002

Phosphite, an analog of phosphate, suppresses the coordinated expression of genes under phosphate starvation.

Phosphate (Pi) and its analog phosphite (Phi) are acquired by plants via Pi transporters. Although the uptake and mobility of Phi and Pi are similar, there is no evidence suggesting that plants can utilize Phi as a sole source of phosphorus. Phi is also known to interfere with many of the Pi starvation responses in plants and yeast (Saccharomyces cerevisiae). In this study, effects of Phi on plant growth and coordinated expression of genes induced by Pi starvation were analyzed. Phi suppressed many of the Pi starvation responses that are commonly observed in plants. Enhanced root growth and root to shoot ratio, a hallmark of Pi stress response, was strongly inhibited by Phi. The negative effects of Phi were not obvious in plants supplemented with Pi. The expression of Pi starvation-induced genes such as LePT1, LePT2, AtPT1, and AtPT2 (high-affinity Pi transporters); LePS2 (a novel acid phosphatase); LePS3 and TPSI1 (novel genes); and PAP1 (purple acid phosphatase) was suppressed by Phi in plants and cell cultures. Expression of luciferase reporter gene driven by the Pi starvation-induced AtPT2 promoter was also suppressed by Phi. These analyses showed that suppression of Pi starvation-induced genes is an early response to addition of Phi. These data also provide evidence that Phi interferes with gene expression at the level of transcription. Synchronized suppression of multiple Pi starvation-induced genes by Phi points to its action on the early molecular events, probably signal transduction, in Pi starvation response.

Arabidopsis↗

PubMed2003

Analysis of the plastidic phosphate translocator gene family in Arabidopsis and identification of new phosphate translocator-homologous transporters, classified by their putative substrate-binding site.

Analysis of the Arabidopsis genome revealed the complete set of plastidic phosphate translocator (pPT) genes. The Arabidopsis genome contains 16 pPT genes: single copies of genes coding for the triose phosphate/phosphate translocator and the xylulose phosphate/phosphate translocator, and two genes coding for each the phosphoenolpyruvate/phosphate translocator and the glucose-6-phosphate/phosphate translocator. A relatively high number of truncated phosphoenolpyruvate/phosphate translocator genes (six) and glucose-6-phosphate/phosphate translocator genes (four) could be detected with almost conserved intron/exon structures as compared with the functional genes. In addition, a variety of PT-homologous (PTh) genes could be identified in Arabidopsis and other organisms. They all belong to the drug/metabolite transporter superfamily showing significant similarities to nucleotide sugar transporters (NSTs). The pPT, PTh, and NST proteins all possess six to eight transmembrane helices. According to the analysis of conserved motifs in these proteins, the PTh proteins can be divided into (a) the lysine (Lys)/arginine group comprising only non-plant proteins, (b) the Lys-valine/alanine/glycine group of Arabidopsis proteins, (c) the Lys/asparagine group of Arabidopsis proteins, and (d) the Lys/threonine group of plant and non-plant proteins. None of these proteins have been characterized so far. The analysis of the putative substrate-binding sites of the pPT, PTh, and NST proteins led to the suggestion that all these proteins share common substrate-binding sites on either side of the membrane each of which contain a conserved Lys residue.

Amino Acid Sequence↗

PubMed2004

Promoter analysis of the barley Pht1;1 phosphate transporter gene identifies regions controlling root expression and responsiveness to phosphate deprivation.

Previous studies have shown that the promoter from the barley (Hordeum vulgare) phosphate transporter gene, HvPht1;1, activates high levels of expression in rice (Oryza sativa) roots and that the expression level was induced by up to 4-fold in response to phosphorus (P) deprivation. To identify promoter regions controlling gene regulation specificities, successive promoter truncations were made and attached to reporter genes. Promoters of between 856 and 1,400 nucleotides activated gene expression in a number of cell types but with maximal expression in trichoblast (root hair) cells. For shorter promoters the trichoblast specificity was lost, but in other tissues the distribution pattern was unchanged. The low P induction response was unaffected by promoter length. Domain exchange experiments subsequently identified that the region between -856 and -547 nucleotides (relative to the translational start) is required for epidermal cell expression. A second region located between 0 and -195 nucleotides controls root-tip expression. The HvPht1;1 promoter contains one PHO-like motif and three motifs similar to the dicot P1BS element. Analysis of promoters from which the PHO-like element was eliminated (by truncation) showed no change in the gene induction response to P deficiency. In contrast, mutation of the P1BS elements eliminated any induction of gene expression in response to low P. An internal HvPht1;1 promoter fragment, incorporating a single P1BS element, had an increased response to P deprivation in comparison with the unmodified promoter (containing three elements). Together these findings further our understanding of the regulation of the HvPht1;1 gene and provide direct evidence for a functional role of the P1BS element in the expression of P-regulated genes.

Amino Acid Motifs↗

PubMed2000

Zinc deficiency up-regulates expression of high-affinity phosphate transporter genes in both phosphate-sufficient and -deficient barley roots.

Phosphate (P) is taken up by plants through high-affinity P transporter proteins embedded in the plasma membrane of certain cell types in plant roots. Expression of the genes that encode these transporters responds to the P status of the plants, and their transcription is normally tightly controlled. However, this tight control of P uptake is lost under Zn deficiency, leading to very high accumulation of P in plants. We examined the effect of plant Zn status on the expression of the genes encoding the HVPT1 and HVPT2 high-affinity P transporters in barley (Hordeum vulgare L. cv Weeah) roots. The results show that the expression of these genes is intimately linked to the Zn status of the plants. Zn deficiency induced the expression of genes encoding these P transporters in plants grown in either P-sufficient or -deficient conditions. Moreover, the role of Zn in the regulation of these genes is specific in that it cannot be replaced by manganese (a divalent cation similar to Zn). It appears that Zn plays a specific role in the signal transduction pathway responsible for the regulation of genes encoding high-affinity P transporters in plant roots. The significance of Zn involvement in the regulation of genes involved in P uptake is discussed.

Carrier Proteins↗

PubMed2005

The characterization of novel mycorrhiza-specific phosphate transporters from Lycopersicon esculentum and Solanum tuberosum uncovers functional redundancy in symbiotic phosphate transport in solanaceous species.

Solanaceous species are among the >200 000 plant species worldwide forming a mycorrhiza, that is, a root living in symbiosis with soil-borne arbuscular-mycorrhizal (AM) fungi. An important parameter of this symbiosis, which is vital for ecosystem productivity, agriculture, and horticulture, is the transfer of phosphate (Pi) from the AM fungus to the plant, facilitated by plasma membrane-spanning Pi transporter proteins. The first mycorrhiza-specific plant Pi transporter to be identified, was StPT3 from potato [Nature414 (2004) 462]. Here, we describe novel Pi transporters from the solanaceous species tomato, LePT4, and its orthologue StPT4 from potato, both being members of the Pht1 family of plant Pi transporters. Phylogenetic tree analysis demonstrates clustering of both LePT4 and StPT4 with the mycorrhiza-specific Pi transporter from Medicago truncatula [Plant Cell, 14 (2002) 2413] and rice [Proc. Natl Acad. Sci. USA, 99 (2002) 13324], respectively, but not with StPT3, indicating that two non-orthologous mycorrhiza-responsive genes encoding Pi transporters are co-expressed in the Solanaceae. The cloned promoter regions from both genes, LePT4 and StPT4, exhibit a high degree of sequence identity and were shown to direct expression exclusively in colonized cells when fused to the GUS reporter gene, in accordance with the abundance of LePT4 and StPT4 transcripts in mycorrhized roots. Furthermore, extensive sequencing of StPT4-like clones and subsequent expression analysis in potato and tomato revealed the presence of a close paralogue of StPT4 and LePT4, named StPT5 and LePT5, respectively, representing a third Pi transport system in solanaceous species which is upregulated upon AM fungal colonization of roots. Knock out of LePT4 in the tomato cv. MicroTom indicated considerable redundancy between LePT4 and other Pi transporters in tomato.

Biological Transport, Active↗

PubMed1980

Selective changes in enzymes of the sn-glycerol 3-phosphate and dihydroxyacetone-phosphate pathways of triacylglycerol biosynthesis during differentiation of 3T3-L1 preadipocytes.

Enzyme activities of the sn-glycerol 3-phosphate (glycerol-P) and of the dihydroxyacetone-phosphte (DHAP) pathway of glycerolipid biosynthesis were investigated during the differentiation of 3T3-L1 preadipocytes into adipocytes. Total particulate glycerol-P and DHAP acyltransferase activities increased 70- and 30-fold, respectively, during differentiation induced with methylisobutylxanthine and dexamethasone. The N-ethylmaleimide-sensitive (microsomal) glycerol-P and DHAP acyltransferase activities were virtually undetectable in nondifferentiated cells, and increased in parallel over 70-fold during differentiation. These and several kinetic observations are consistent with the induction of a single microsomal enzyme having dual activity. During differentiaion, the N-ethylmaleimide-resistant DHAP acyltransferase activity increased 10-fold, suggesting the presence of at least two DHAP acyltransferase isoenzymes. Qualitatively similar changes in microsomal glycerol-P and DHAP acyltransferase activities were observed when cell differentiation was induced with insulin or with insulin plus dexamethasone and methylisobutylxanthine. Acyl-DHAP oxidoreductase (EC 1.1.1.101) specific activity increased only 3- to 5-fold during adipocyte differentiation. Alkyl-DHAP synthase activity was not detected. These data demonstrate that selective changes in enzyme activities of the gycerol-P pathways of glycerolipid synthesis occur during the differentiation of 3T3-L1 preadipocytes.

1-Methyl-3-isobutylxanthine↗

PubMed1992

Phosphate efflux from jejunal enterocytes of the rat: effect of phosphate concentration gradient and pH.

The effect of variation in the intracellular and extracellular phosphate concentration on the Pi efflux across the basolateral membrane of pre-loaded enterocytes has been examined. Efflux rate constants for Pi fell from 0.89 h-1 to 0.68 h-1 as the extracellular Pi concentration was increased from 0.5 mM to 5 mM. As the intracellular Pi concentration was raised from 0.5 to 3 mM the rate constant dropped from 0.95 h-1 to 0.77 h-1. The findings are indicative of the presence of Pi-specific transporter at the basolateral membrane. The efflux rate constant of Pi at pH 7.1 was higher than that at pH 7.4 suggesting that the Pi flux across the basolateral membrane of enterocytes follows a similar pattern towards pH changes as do fluxes across the brush-border membrane.

Animals↗