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H Murer

Publications and source records attributed to H Murer.

At least 109 records · Page 6Linked to original sources
PubMed1997

Abnormal sulfate metabolism in vitamin D-deficient rats.

To explore the possibility that vitamin D status regulates sulfate homeostasis, plasma sulfate levels, renal sulfate excretion, and the expression of the renal Na-SO4 cotransporter were evaluated in vitamin D-deficient (D-D-) rats and in D-D- rats rendered normocalcemic by either vitamin D or calcium/lactose supplementation. D-D- rats had significantly lower plasma sulfate levels than control animals (0.93+/-0.01 and 1.15+/-0.05 mM, respectively, P < 0.05), and fractional sulfate renal excretion was approximately threefold higher comparing D-D- and control rats. A decrease in renal cortical brush border membrane Na-SO4 cotransport activity, associated with a parallel decrease in both renal Na-SO4 cotransport protein and mRNA content (78+/-3 and 73+/-3% decreases, respectively, compared with control values), was also observed in D-D- rats. Vitamin D supplementation resulted in a return to normal of plasma sulfate, fractional sulfate excretion, and both renal Na-SO4 cotransport mRNA and protein. In contrast, renal sulfate excretion and renal Na-SO4 cotransport activity, protein abundance, and mRNA remained decreased in vitamin D-depleted rats fed a diet supplemented with lactose and calcium, despite that these rats were normocalcemic, and had significantly lower levels of parathyroid hormone and 25(OH)- and 1,25(OH)2-vitamin D levels than the vitamin D-supplemented groups. These results demonstrate that vitamin D modulates renal Na-SO4 sulfate cotransport and sulfate homeostasis. The ability of vitamin D status to regulate Na-SO4 cotransport appears to be a direct effect, and is not mediated by the effects of vitamin D on plasma calcium or parathyroid hormone levels. Because sulfate is required for synthesis of essential matrix components, abnormal sulfate metabolism in vitamin D-deficient animals may contribute to producing some of the abnormalities observed in rickets and osteomalacia.

Animals↗
PubMed1997

Parathyroid hormone-dependent degradation of type II Na+/Pi cotransporters.

Parathyroid hormone (PTH) inhibits proximal tubular brush border membrane Na+/Pi cotransport activity; this decrease in the transport activity was found to be associated with a decrease in type II Na+/Pi cotransporter protein content in rat brush border membranes. In the present study we investigated the PTH-dependent regulation of the type II Na+/Pi cotransporter in opossum kidney cells, a previously established model to study cellular mechanisms involved in the regulation of proximal tubular Na+/Pi cotransport. We transfected opossum kidney cells with a cDNA coding for NaPi-2 (rat renal type II Na+/Pi cotransporter). This allowed the study of PTH-dependent regulation of the transfected NaPi-2 and of the corresponding intrinsic cotransporter (NaPi-4). The results show (i) that the intrinsic and the transfected cotransporters are functionally (transport) and morphologically (immunofluorescence) localized at the apical membrane, (ii) that the intrinsic as well as the transfected Na+/Pi cotransport activities are inhibited by PTH, (iii) that PTH leads to a retrieval of both cotransporters from the apical membrane, (iv) that both cotransporters are rapidly degraded in response to PTH, and (v) that the reappearance/recovery of type II Na+/Pi cotransporter protein and function from PTH inhibition requires de novo protein synthesis. These results document that PTH leads to a removal of type II Na+/Pi cotransporters from the apical membrane and to their subsequent degradation.

Animals↗
PubMed1997

Membrane traffic and control of proximal tubular sodium phosphate (Na/Pi)-cotransport.

Phosphate (P(i)) is freely filtered at the glomerular capillaries and largely reabsorbed in the proximal tubule by a Na-dependent, secondary active transport mechanism. Two different brush border membrane Na/P(i)-cotransporters have recently been "cloned" (type I and type II). Only the type II transporter undergoes physiological regulation (e.g., diet, acid/base, parathyroid hormone); it is also involved in pathophysiological alterations of renal Pi-handling (e.g., X-linked hypophosphatemia). In recent experiments on rats and on tissue culture cells (Opossum kidney cells, OK cells) id was documented that manoeuvres leading to increased uptake involve membrane insertion (fast changes) and new synthesis of type II transporters (slow changes), whereas decreased Na/Pi-cotransport activity is associated with their specific membrane retrieval (fast changes) and lysosomal degradation (slow changes).

Animals↗
PubMed1997

Role of microtubules in the rapid regulation of renal phosphate transport in response to acute alterations in dietary phosphate content.

Renal proximal tubular response to acute administration of a low Pi diet is characterized by a rapid adaptive increase in apical brush border membrane (BBM) Na-Pi cotransport activity and Na-Pi cotransporter protein abundance, independent of a change in Na-Pi cotransporter mRNA levels (Levi, M., M. Lötscher, V. Sorribas, M. Custer, M. Arar, B. Kaissling, H. Murer, and J. Biber. 1994. Am. J. Physiol. 267: F900-F908). The purposes of the present study were to determine if the acute adaptive response occurs independent of de novo protein synthesis, and if microtubules play a role in the rapid upregulation of the Na-Pi cotransporters at the apical BBM. We found that inhibition of transcription by actinomycin D and translation by cycloheximide did not prevent the rapid adaptive response. In addition, in spite of a 3.3-fold increase in apical BBM Na-Pi cotransporter protein abundance, there was no change in cortical homogenate Na-Pi cotransporter protein abundance. Pretreatment with colchicine, which resulted in almost complete disruption of the microtubular network, abolished the adaptive increases in BBM Na-Pi cotransport activity and Na-Pi cotransporter protein abundance. In contrast, colchicine had no effect on the rapid downregulation of Na-Pi cotransport in response to acute administration of a high Pi diet. We conclude that the rapid adaptive increase in renal proximal tubular apical BBM Na-Pi cotransport activity and Na-Pi cotransporter abundance is independent of de novo protein synthesis, and is mediated by microtubule-dependent translocation of presynthesized Na-Pi cotransporter protein to the apical BBM.

Adaptation, Physiological↗
PubMed1997

Identification of a cDNA/protein leading to an increased Pi-uptake in Xenopus laevis oocytes.

In a previous report we documented an increased Na(+)-dependent transport of inorganic phosphate (P(i)) in Xenopus laevis oocytes injected with mRNA isolated from rabbit duodenum (Yagci et al., Pfluegers Arch. 422:211-216, 1992; ref 24). In the present study we have used expression cloning in oocytes to search for the cDNA/mRNA involved in this effect. The identified cDNA (provisionally named PiUS; for P(i)-uptake stimulator) lead to a 3-4-fold stimulation of Na(+)-dependent P(i)-uptake (10ng cRNA injected, 3-5 days of expression). Na(+)-independent uptake of P(i) was also affected but transport of sulphate and L-arginine (in the presence or absence of sodium) remained unchanged. The apparent K(m)-values for the induced Na(+)-dependent uptake were 0.26 +/- 0.04 mM for P(i) and 14.8 +/- 3.0 mM for Na+. The 1796 bp cDNA codes for a protein of 425 amino acids. Hydropathy analysis suggests a lack of transmembrane segments. In vitro translation resulted in a protein of 60 kDa and provided no evidence of glycosylation. In Northern blots a mRNA of approximately 2 kb was recognized in various tissues including different intestinal segments, kidney cortex, kidney medulla, liver and heart. Homology searches showed no similarity to proteins involved in membrane transport and its control. In conclusion, we have cloned from a rabbit small intestinal cDNA library a novel cDNA encoding a protein stimulating P(i)-uptake into Xenopus laevis oocytes, but which is not a P(i)-transporter itself.

Amino Acid Sequence↗
PubMed1997

Renal endosomal phosphate (Pi) transport in normal and diabetic rats and response to chronic Pi deprivation.

Chronic renal adaptation to dietary deprivation of Pi is accompanied by increased Na+/Pi co-transport across the brush border membrane of the renal proximal tubule. The increased activity of this co-transport system depends on de novo protein synthesis and insulin. The present study used normal and diabetic rats to determine if the endosomal pool of Na+/Pi co-transporters was altered by Pi deprivation and the possible role of insulin. In response to 5 days of dietary Pi deprivation there was a significant increase in endosomal Na+/Pi co-transport in control rats but there was no change in diabetic rats. The increase in endosomal Pi uptake was restored in diabetic rats treated with exogenous insulin. Na(+)-independent Pi uptake and proline uptake remained unchanged in all groups. The changes in endosomal Na+/Pi co-transport correlated with the abundance of the specific Na+/Pi co-transporter protein, as determined by Western blots. The pattern of endosomal changes paralleled that observed in brush border membranes. One possibility consistent with these findings is that the endosomal fraction contains newly synthesized Na+/Pi co-transporters targeted for delivery to the apical brush border membrane. Increased synthesis and delivery is required to maintain the adaptation to chronic Pi deprivation.

Animals↗
PubMed1997

A molecular view of proximal tubular inorganic phosphate (Pi) reabsorption and of its regulation.

In recent years, two mammalian proximal tubular brush border membrane Na/Pi cotransporters (types I and II) have been structurally identified by expression cloning techniques. Oocyte expression studies have shown that only the transport characteristics of the type II transporter correspond to the well-known properties of proximal tubular brush border membrane of Pi transport. In studies on physiological regulation by hormonal and non-hormonal factors a direct involvement and determining role of the type II transporter has been documented. Most interestingly, specific membrane retrieval/insertion phenomena participate in acute (minutes/hours) adjustments of brush border membrane Na/Pi cotransport rates; for chronic (hours/days) alterations also specific resynthesis/degradation processes participate. In pathophysiological alterations (e.g. in X-linked hypophosphataemia and in heavy metal-induced nephrotoxicity) the expression of the type II Na/Pi cotransporters is reduced and explains the observed phosphaturia.

Absorption↗
PubMed1997

Regulation of the transfected Na+/H+-exchanger NHE3 in MDCK cells by vasotocin.

NHE3 is most likely the isoform involved in renal reabsorption of HCO3- and Na+. The functional properties of the "cloned" NHE3 isoform, including its transport regulation by extra- and intracellular stimuli, have so far been studied using non-epithelial expression systems. In the present report we stably transfected NHE3 cDNA (rabbit isoform) into Madin-Darby canine kidney cells (MDCK) cells and compared the sensitivity to inhibitors and the regulation of the Na+/H+-exchanger by vasotocin in NHE3 transfectants to that of the intrinsic basolateral Na+/H+-exchanger in untransfected and control transfected MDCK cells. By Southern blot analysis we documented that the NHE3 transcript is expressed in NHE3 transfectants. Na+/H+-exchange activity, measured as sodium-dependent recovery of intracellular pH from an acid load using 2', 7'-bis(carboxymethyl)-5(6)-carboxy-fluorescein (BCECF), was equally present at the basolateral cell surface of all cell lines; however, NHE3 transfectants demonstrated transport activity in the apical membrane that was significantly higher than that in untransfected or control transfected MDCK cells. Studies with ethylisopropylamiloride (EIPA) have shown that there is a similar sensitivity to inhibitors of the apical and/or basolateral Na+/H+-exchanger in transfected and untransfected MDCK cell lines. In contrast, the apical Na+/H+-exchanger (as compared to the basolateral Na+/H+-exchanger) of NHE3 transfectants was found to be relatively insensitive to the inhibitor HOE 694. Vasotocin decreased the activity of the apical Na+/H+-exchanger in NHE3 transfectants and stimulated the activity of the basolateral Na+/H+-exchanger in transfected (with NHE3 or pMAMneo) and untransfected MDCK cells. Phorbol ester, as expected, increased the activity of the Na+/H+-exchanger in the basolateral membrane of all cell lines; also, it stimulated transport activity at the apical cell surface of NHE3 transfectants. No change of Na+/H+-exchange activities was seen in studies with 8-bromo-cAMP. The PKC inhibitor calphostin C completely suppressed regulation of the apical and/or basolateral Na+/H+-exchanger by vasotocin, it partially blocked activation of the apical Na+/H+-exchanger in NHE3 transfectants by phorbol 12-myristate 13-acetate (PMA), and completely blocked stimulation of basolateral Na+/H+-exchanger by PMA. Consistent with a V1 receptor action, the effects of vasotocin in NHE3 transfectants and in MDCK cells were blocked by the V1 receptor antagonist, d(CH2)5Tyr(Me)-AVP, but were not reproduced by the V2 receptor agonist desmopressin. It is concluded that NHE3 in the apical membrane of NHE3-transfected MDCK cells contributes to the differential regulation of the apical and basolateral Na+/H+-exchanger by vasotocin; NHE3 is inhibited and endogenous Na+/H+-exchange activity is stimulated by vasotocin via V1 receptor activation of the protein kinase C pathway.

Animals↗
PubMed1997

A putative growth-related renal Na(+)-Pi cotransporter.

The mRNA that encodes for NaPi-2, the renal Na(+)-Pi cotransporter that is upregulated by Pi depletion in the adult rat, is low in the young animal. Yet, renal Na-Pi cotransport rates are higher in rapidly growing than in fully grown rats. The aim of this study was to unravel the molecular basis of this apparent discrepancy. Poly(A) RNA obtained from the renal cortex of young animals induced higher rates of Na(+)-Pi cotransport in oocytes than equal amounts of poly(A) mRNA obtained from the renal cortex of mature rats. Moreover, poly(A) RNA obtained from renal cortex of rapidly growing animals treated with antisense NaPi-2 oligomers or depleted of NaPi-2 transcripts by subtractive hybridization with cDNA generated from the renal cortex of adult rats retained its ability to induce Na(+)-Pi cotransport in oocytes. In addition, renal poly(A) RNA of the young subjected to subtraction hybridization generated a 379-base pair reverse transcriptase-polymerase chain reaction product common to all known type II Na(+)-Pi cotransporters. These observations permit us to surmise that the high rates of Na(+)-Pi cotransport prevailing during growth are due, at least in part, to the expression of a specific mRNA that is only partially homologous to that of NaPi-2.

Aging↗
PubMed1997

Differentiation and cell polarity during renal cyst formation in the Han:SPRD (cy/+) rat, a model for ADPKD.

Despite the recent positional cloning of genes responsible for autosomal dominant polycystic kidney disease (ADPKD), the exact pathogenetic mechanisms underlying this disorder are still unclear. To learn more about cyst formation, we investigated cell differentiation and cell polarity in the Han:SPRD (cy/+) rat between 21 days and 60 wk of age. At early stages of cyst development, alkaline phosphatase, aquaporin-1, NaSi-1 cotransporter, and Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) were expressed normally. Clusterin mRNA was only sparsely expressed at the onset of cystic degeneration and increased thereafter, being highest in noncystic nephron segments. In cyst wall cells, clusterin on the one hand and alkaline phosphatase, aquaporin-1, NaSi-1-cotransporter, and Na(+)-K(+)-ATPase on the other were expressed in a mutually exclusive fashion. No change in cell polarity could be observed at any stage. Our data therefore argue against a change in cell polarity and against an early arrest in normal tubular development during cyst formation in the Han:SPRD (cy/+) rat model of ADPKD but favor the hypothesis that tubular epithelia develop in an orderly fashion and degenerate thereafter.

Aging↗
PubMed1997

Acid-induced stimulation of Na-Pi cotransport in OK cells: molecular characterization and effect of dexamethasone.

Alterations in systemic acid/base balance affect renal Pi excretion. In the present study, the effects of an acidic pH on apical Na-dependent Pi (Na-Pi) cotransport were analyzed using OK cells (opossum kidney cell line). Cells were maintained at either pH 7.4 or 7.1 (altered HCO3- concentration at constant PCO2). Incubation in acidic medium led to an increase in Na-Pi cotransport activity, which was characterized by a transient, initial response (2-4 h, 25% increase) followed by a sustained response (24 h, 75% increase). Increased Na-Pi cotransport activity (24 h) was sensitive to inhibition by parathyroid hormone. Actinomycin D did not abolish the acid-induced increases (initial and sustained responses). Cycloheximide abolished the increase in Na-Pi cotransport observed after 24 h. The increase in Na-Pi cotransport (24 h) was prevented by dexamethasone (2 x 10(-6) M). Western blots showed a twofold (3 h) and two- to threefold (24 h) increase in NaPi-4 protein after acid exposure. Cycloheximide prevented the late increase in NaPi-4 protein abundance. Also dexamethasone reduced the increase in specific protein content. In conclusion, the exposure of OK cells to an acidic medium causes a stimulation of the NaPi-4 cotransporter that is prevented by dexamethasone.

Animals↗
PubMed1997

Identification of a new gene product (diphor-1) regulated by dietary phosphate.

Chronic restriction of dietary Pi elicits an increased reabsorption of Pi in the kidney proximal tubules, which involves a stimulation of apical Na-Pi cotransport. This adaptation is in part a direct cellular response of which the mechanism(s) are poorly understood. In this study, the impact of dietary Pi restriction on the differential expression of rat kidney cortex mRNAs was visualized to identify gene products regulated by the Pi status. When kidney cortex mRNAs of rats fed a low- or a high-Pi diet were compared by differential display-polymerase chain reaction (DD-PCR), thirty modulated cDNA bands were observed, of which four were confirmed as being regulated. We focused on one of the upregulated bands, dietary Pi-regulated RNA-1 (diphor-1). A cDNA containing an open reading frame encoding a 52-kDa protein was cloned by library screening. Diphor-1 exhibits a high degree of identity to the Na/H exchanger regulatory factor and to a tyrosine kinase activating protein. Highest expression of diphor-1 mRNA was detected in the kidney (proximal tubules) and in small intestine. Expression experiments showed that diphor-1 specifically increases Na-Pi cotransport in oocytes of Xenopus laevis coinjected with renal type II Na-Pi contransporter cRNA. Further characterizations of diphor-1 will show whether diphor-1 is primarily or secondarily involved in the response to dietary Pi.

Amino Acid Sequence↗
PubMed1997

Effect of glucocorticoids on neonatal rabbit renal cortical sodium-inorganic phosphate messenger RNA and protein abundance.

Administration of glucocorticoids to neonates increases proximal tubule volume absorption by increasing glucose, bicarbonate, and amino acid transport. We have recently demonstrated that glucocorticoids may contribute to the maturational decrease in phosphate transport. This study examines the maturation of NaPi-6 [the regulated proximal tubule sodium-inorganic phosphate (Na-Pi) transporter] mRNA and protein abundance and the mechanism for the decrease in phosphate transport by glucocorticoids. Weaned young rabbits (5 wk) had a 2-fold greater brush border membrane NaPi-6 protein abundance than that measured in adults. Renal cortical NaPi-6 mRNA abundance was comparable in neonates (less than 10 d of age) and adults. Renal brush border membrane vesicles from dexamethasone-treated neonatal rabbits (10 micrograms/100 g of body weight for 4 d) had a lower rate of Na-Pi transport than vehicle-treated controls (46.8 +/- 6.5 versus 71.0 +/- 9.0 pmol 32P/10 s/mg of protein, p < 0.05). Abundance of NaPi-6 protein in brush border membrane vesicles was 3-fold lower in newborn rabbits treated with pharmacologic doses of dexamethasone than in vehicle-treated controls. NaPi-6 mRNA abundance was the same in both groups. NaPi-1, a brush border membrane phosphate transporter which is also an anion channel, mRNA, and protein abundance was not affected by glucocorticoids. These data demonstrate that there is a maturational decrease in NaPi-6 protein abundance and that glucocorticoids decrease neonatal phosphate transport, at least in part, by reducing the number of Na-Pi transporters.

Animals↗
PubMed1997

Polarization of adenosine effects on intracellular pH in A6 renal epithelial cells.

The effect of adenosine on Na+/H+ exchange activity was examined in cultured A6 renal epithelial cells. Adenosine and its analogue N6-cyclopentyladenosine (CPA) had different effects on Na+/H+ exchange activity depending on the side of addition. Basolateral CPA induced a stimulation of Na+/H+ exchange activity that was completely prevented by preincubation with an A2A-selective antagonist, 8-(3-chlorostyryl)caffeine, whereas apical CPA induced a slight but significant inhibition of Na+/H+ exchange activity that was significantly reduced by the A1-receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine. Protein kinase C activation may be involved in mediating the apical CPA inhibition of Na+/H+ exchange activity; this inhibition was prevented by the protein kinase C inhibitor calphostin C. Treatment with either forskolin or 8-bromo-cAMP significantly stimulated Na+/H+ exchange activity; only basolateral CPA addition induced an increase in cAMP level. These observations together with the finding that the CPA-dependent stimulation of exchange activity was prevented by the protein kinase A inhibitor H-89 support the hypothesis that basolateral CPA stimulates Na+/H+ exchange via adenylate cyclase/protein kinase A activation. Basolateral CPA also increased transepithelial Na+ transport, and this stimulation was prevented by the Na+/H+ exchange inhibitor HOE-694, suggesting that changes in pHi during hormone action can act as an intermediate in the second-messenger cascade.

Adenosine↗
PubMed1996

Structure of murine and human renal type II Na+-phosphate cotransporter genes (Npt2 and NPT2).

Na+-phosphate (Pi) cotransport across the renal brush border membrane is the rate limiting step in the overall reabsorption of filtered Pi. Murine and human renal-specific cDNAs (NaPi-7 and NaPi-3, respectively) related to this cotransporter activity (type II Na+-Pi cotransporter) have been cloned. We now report the cloning and characterization of the corresponding mouse (Npt2) and human (NPT2) genes. The genes were cloned by screening mouse genomic and human chromosome 5-specific libraries, respectively. Both genes are approximately 16 kb and are comprised of 13 exons and 12 introns, the junctions of which conform to donor and acceptor site consensus sequences. Putative CAAT and TATA boxes are located, respectively, at positions -147 and -40 of the Npt2 gene and -143 and -51 of the NPT2 gene, relative to nucleotide 1 of the corresponding cDNAs. The translation initiation site is within exon 2 of both genes. The first 220 bp of the mouse and human promoter regions exhibit 72% identity. Two transcription start sites (at positions -9 and - 10 with respect to nucleotide 1 of NaPi-7 cDNA) and two polyadenylylation signals were identified in the Npt2 gene by primer extension, 5' and 3' rapid amplification of cDNA ends (RACE). A 484-bp 5' flanking region of the Npt2 gene, comprising the CAAT box, TATA box, and exon 1, was cloned upstream of a luciferase reporter gene; this construct significantly stimulated luciferase gene expression, relative to controls, when transiently transfected into OK cells, a renal cell line expressing type II Na+ -Pi cotransporter activity. The present data provide a basis for detailed analysis of cis and trans elements involved in the regulation of Npt2/NPT2 gene transcription and facilitate screening for mutations in the NPT2 gene in patients with autosomally inherited disorders of renal Pi reabsorption.

Animals↗
PubMed1996

Expression of a renal type I sodium/phosphate transporter (NaPi-1) induces a conductance in Xenopus oocytes permeable for organic and inorganic anions.

Two distinct molecular types (I and II) of renal proximal tubular brush border Na+/Pi cotransporters have been identified by expression cloning on the basis of their capacity to induce Na+-dependent Pi influx in tracer experiments. Whereas the type II transporters (e.g., NaPi-2 and NaPi-3) resemble well known characteristics of brush border Na+/Pi cotransport, little is known about the properties of the type I transporter (NaPi-1). In contrast to type II, type I transporters produced electrogenic transport only at high extracellular Pi concentrations (> or =3 mM). On the other hand, expression of NaPi-1 induced a Cl- conductance in Xenopus laevis oocytes, which was inhibited by Cl- channel blockers [5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) > niflumic acid >> 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid]. Further, the Cl- conductance was inhibited by the organic anions phenol red, benzylpenicillin (penicillin G), and probenecid. These organic anions induced outwardly directed currents in the absence of Cl-. In tracer studies, we observed uptake of benzylpenicillin with a Km of 0.22 mM; benzylpenicillin uptake was inhibited by NPPB and niflumic acid. These findings suggest that the type I Na+/Pi cotransporter functions also as a novel type of anion channel permeable not only for Cl- but also for organic anions. Such an apical anion channel could serve an important role in the transport of Cl- and the excretion of anionic xenobiotics.

Animals↗
PubMed1996

In vivo suppression of the renal Na+/Pi cotransporter by antisense oligonucleotides.

A 20-mer phosphorothioate oligonucleotide (AS1) was designed to hybridize to the message for the rat kidney sodium phosphate cotransporter NaPi-2 close to the translation initiation site. Single intravenous doses of this oligonucleotide were given to rats maintained on a low phosphorus diet to increase NaPi-2 expression. At 3 days after oligonucleotide infusion, rats receiving 2.5 micromol of AS1 exhibited a reduction in renal NaPi-2 to cyclophilin mRNA ratio by 40% +/- 17%, and rats receiving 7.5 micromol of AS1 exhibited a reduction in NaPi-2 to cyclophilin mRNA ratio by 46% +/- 21%. Reversed-sequence AS1 was without effect. The higher dose of 7.5 micromol of AS1 also reduced the rate of phosphate uptake into renal brush border membrane vesicles and the expression of NaPi-2 protein detected by Western blotting in these vesicles. Reversed sequence AS1 was again without effect on these parameters. These results suggest that systemically infused oligonucleotides can exert antisense effects in the renal proximal tubule.

Animals↗