Role of glucocorticoids in the maturation of renal cortical Na+/H+ exchanger activity during fetal life in sheep

1995 ◽  
Vol 268 (4) ◽  
pp. F710-F717 ◽  
Author(s):  
E. N. Guillery ◽  
L. P. Karniski ◽  
M. S. Mathews ◽  
W. V. Page ◽  
J. Orlowski ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Renal Cortex ◽  
Membrane Vesicles ◽  
Sodium Reabsorption ◽  
Fetal Life ◽  
Maximal Velocity ◽  
Mrna Levels ◽  
Significant Difference ◽  
Microvillus Membrane

We have studied the role of glucocorticoids in inducing the maturation in activity of the proximal tubule Na+/H+ exchanger that follows birth. Renal cortical microvillus membrane vesicles were prepared from 132-day gestation sheep fetuses (n = 8) that had received intraperitoneal cortisol (13 micrograms.kg-1.h-1) for the previous 48 h. Membrane vesicles were also obtained from sham-operated twin controls (n = 8). Amiloride-sensitive uptake of 22Na+ by these vesicles was measured, and Woolf-Augustinsson-Hofstee plots were used to determine the Michaelis constant (Km) and maximal velocity (Vmax). There was no significant difference in Km; however, the Vmax was 61% higher in cortisol-treated fetuses. Posttreatment circulating cortisol levels were significantly higher in the treated fetuses. Total RNA was collected from renal cortex of the eight pairs of twins when killed. Renal cortex Na+/H+ exchanger 3 (NHE3) mRNA levels were approximately fourfold higher in cortisol-treated than in control fetuses. Although proximal tubule Na+/H+ exchanger activity and renal cortex NHE3 mRNA levels increased significantly in cortisol-treated fetuses, cortisol infusion did not stimulate renal sodium reabsorption in the fetus but rather produced a natriuresis. These results demonstrate that glucocorticoids can induce an increase in both Na+/H+ exchanger activity and NHE3 mRNA levels during the last trimester of gestation in sheep. However, these changes are not associated with an increased ability of the fetal kidney to reabsorb sodium.

Angiotensin II and the maturation of renal cortical Na+/H+ exchanger activity during fetal life in sheep

1996 ◽  
Vol 271 (6) ◽  
pp. R1507-R1513 ◽  
Author(s):  
E. N. Guillery ◽  
M. S. Mathews ◽  
J. Orlowski ◽  
J. E. Robillard
Keyword(s):  
Angiotensin Ii ◽  
Proximal Tubule ◽  
Membrane Vesicles ◽  
Plasma Renin ◽  
Fetal Life ◽  
Maximal Velocity ◽  
Mrna Levels ◽  
Ang Ii ◽  
The Difference ◽  
Near Term

The postnatal rise in renal Na+ reabsorption is associated with an increase in proximal tubule apical membrane Na+/H+ exchanger (NHE) activity in sheep. Inasmuch as circulating angiotensin II (ANG II) levels increase immediately after birth and ANG II is known to upregulate NHE activity in the adult proximal tubule, we postulated that ANG II plays a role in mediating maturational changes in NHE activity. We therefore studied the effects of ANG II infusion (10 micrograms/h) for 24 h on renal cortical NHE activity in chronically instrumented, twin ovine fetuses (129 +/- 2 days gestation, term is 145 days, n = 10 pairs); one twin of each pair served as a control. After 24 h, the fetuses were killed and brush-border membrane vesicles (BBMV) were prepared from the renal cortices. Postinfusion plasma ANG II levels were significantly higher and plasma renin activities were significantly lower in treated fetuses compared with controls. Kinetic analysis revealed an increase in NHE activity after ANG II treatment; however, the difference was not statistically significant: maximal velocity (in nmol.s-1.mg protein-1) control 1.65 +/- 0.50, treated 2.31 +/- 0.66 (P = 0.11, n = 9 pairs); Michaelis constant control 8.29 +/- 1.17 mM, treated 9.84 +/- 1.26 mM (P = 0.11). Northern blots of total RNA from the cortices of these animals were hybridized to a D-[32P]UTP-labeled antisense RNA probe prepared from a 1.3-kb rat NHE3 cDNA fragment. There were no differences between the groups in NHE3 mRNA levels (32P counts were control 413 +/- 54, treated 340 +/- 46). ANG II does not appear to play an important role in the regulation of NHE activity in the proximal tubule of the near-term sheep fetus.

Maturation of proximal tubule Na+/H+ antiporter activity in sheep during transition from fetus to newborn

1994 ◽  
Vol 267 (4) ◽  
pp. F537-F545 ◽  
Author(s):  
E. N. Guillery ◽  
L. P. Karniski ◽  
M. S. Mathews ◽  
J. E. Robillard
Keyword(s):  
Proximal Tubule ◽  
Developmental Change ◽  
Membrane Vesicles ◽  
Michaelis Constant ◽  
Maturational Change ◽  
Significant Difference ◽  
Microvillus Membrane ◽  
Renal Tubular ◽  
Definition Of ◽  
Kinetics Of

We have studied maturational changes in the kinetics of the proximal tubule Na+/H+ antiporter. Microvillus membrane vesicles were prepared from renal cortex of fetal and newborn lambs. Amiloride-sensitive uptake of 22Na+ by these vesicles was measured and Woolf-Augustinsson-Hofstee plots were used to determine the Michaelis constant (Km) and rate of maximal uptake (Vmax). Initial studies of fetal lambs at 130-132 days gestation (n = 5; term is 145 days) and 3- to 4-day-old lambs (n = 5) revealed no maturational change in Km (7.27 +/- 1.25 for fetuses and 9.01 +/- 1.03 mM for lambs); however, there was a 242% increase in Vmax (from 1.28 +/- 0.33 in the fetuses to 4.37 +/- 0.85 nmol.s-1.mg protein-1 in the lambs, P = 0.005). Further definition of the developmental change in Na+/H+ antiporter Vmax was obtained when 144-day-gestation fetuses (n = 5) were compared with 24-h-old sibling lambs (n = 5) that had been delivered by cesarean section at 144 days gestation. Again, no significant difference was seen in Na+/H+ antiporter Km (14.9 +/- 6.5 for fetuses and 12.5 +/- 3.4 mM for lambs); however, a significant increase in Na+/H+ antiporter Vmax occurred (from 1.41 +/- 0.51 in the fetuses to 3.32 +/- 0.37 nmol.s-1.mg protein-1 in the lambs, P < 0.01). This study shows that there is a maturational increase in renal cortical Na+/H+ antiporter Vmax during the transition from fetal to newborn life. This increase parallels the increase in renal tubular Na+ reabsorption that occurs at this time.

Renal Na+/H+ exchanger isoforms and their regulation by thyroid hormone

1996 ◽  
Vol 270 (2) ◽  
pp. C585-C592 ◽  
Author(s):  
K. K. Azuma ◽  
D. F. Balkovetz ◽  
C. E. Magyar ◽  
L. Lescale-Matys ◽  
Y. Zhang ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Proximal Tubule ◽  
Renal Cortex ◽  
Blot Hybridization ◽  
Mrna Level ◽  
Kinetic Studies ◽  
Hormone Treatment ◽  
Mrna Levels ◽  
Thyroid Status ◽  
Significant Difference

Na+ crosses the luminal membrane of the proximal tubule primarily via Na+/H+ exchange (NHE), and NHE activity is influenced by thyroid status. Pharmacological, immunological, and kinetic studies indicate multiple isoforms of NHE, and four full-length cDNAs have been cloned to date. The aims of this study were to determine which NHE mRNAs (NHE1, -2, -3, and -4) were expressed in the rat proximal tubule, the relative abundance of each in the renal cortex, and the effect of thyroid status on their expression. By blot hybridization of poly(A)+ RNA, all NHE isoform mRNAs were detected in the rat renal cortex; NHE1, -2, and -3 in the proximal tubule; and NHE1 and -3 in LLC-PK1 cells. NHE3 mRNA abundance was fourfold higher than the other three isoforms in renal cortex. The effect of thyroid status was assessed in renal cortex from euthyroid, hypothyroid, and hyperthyroid rats. Although none of the NHE mRNA levels was altered in the transition from euthyroid to hypothyroid states, both NHE2 and NHE3 mRNA levels increased 1.5-fold in the transition from hypo- to hyperthyroidism. NHE3 protein, measured by immunoblot with the use of an NHE3-specific antibody, was detected at 83-85 kDa in renal cortex and codistributed on sorbitol gradients with the brush-border marker alkaline phosphatase. No significant difference in NHE3 protein abundance was detected between hypothyroid and hyperthyroid rats. In conclusion, in the renal cortex, the NHE3 isoform predominates at the mRNA level, is expressed in apical membranes, and increases at the mRNA but not the protein levels in response to thyroid hormone treatment, suggesting parallel changes in synthesis and turnover of NHE3 by thyroid hormone.

Modifier role of internal H+ in activating the Na+–H+ exchanger in renal microvillus membrane vesicles

Nature ◽  
1982 ◽  
Vol 299 (5879) ◽  
pp. 161-163 ◽  
Author(s):  
Peter S. Aronson ◽  
Jeannette Nee ◽  
Marjorie A. Suhm
Keyword(s):  
Membrane Vesicles ◽  
Microvillus Membrane

Nfy-c expression in colorectal cancer

2009 ◽  
Vol 27 (15_suppl) ◽  
pp. e15086-e15086
Author(s):  
A. E. Kottorou ◽  
A. G. Antonacopoulou ◽  
L. Skarlas ◽  
P. D. Grivas ◽  
C. D. Scopa ◽  
...  
Keyword(s):  
Colorectal Cancer ◽  
Disease Recurrence ◽  
Clinicopathological Parameters ◽  
Mrna Levels ◽  
Nuclear Factor ◽  
Expression Levels ◽  
Nuclear Factor Y ◽  
Significant Difference ◽  
Tissue Specimens

e15086 Background: Nuclear factor Y- C (NFY-C) gene encodes one of the three subunits of nuclear factor Y, a highly conserved transcription factor which binds to the promoters of a variety of genes, which are implicated in cell cycle progression, drug metabolism and antigen presentation. The purpose of the current study was to investigate the role of NFY-C in colorectal cancer by evaluating its mRNA expression in both malignant and normal colonic tissue from patients with colorectal carcinomas with and without disease relapse. Methods: Publicly available expression microarray data were analyzed to reveal elevated levels of NFY-C in patients with colorectal carcinoma who relapsed compared to patients who remained disease free. The mRNA levels of NFY-C were evaluated by quantitative RT-PCR in 81 neoplastic colorectal tissue specimens and 23 normal tissue specimens from patients with colorectal cancer who had undergone curative resections at the University Hospital of Patras, Greece, between 1995 and 2005. The mRNA levels were analysed in relation to clinicopathological parameters. Results: No significant difference was found in the expression levels of NFY-C between normal and malignant tissues. The expression levels of NFY-C were not related to age, gender, grade, stage or primary site of the disease. However, a statistically significant difference (p=0.02) was observed in NFY-C levels between patients with and without disease recurrence. More specifically, patients with low NFY-C levels relapsed more often than patients who overexpressed NFY-C. Nevertheless, the expression was not related to time to disease progression. Finally, patients with higher NFY-C expression levels seem to have improved survival, compared to patients with low NFY-C expression levels although the difference was not statistically significant. Conclusions: Expression levels of NFY-C seem to be associated with disease recurrence. The role of NFY-C in colorectal cancer warrants further investigation. No significant financial relationships to disclose.

Effect of glucocorticoids on renal cortical NHE-3 and NHE-1 mRNA

1994 ◽  
Vol 267 (3) ◽  
pp. F437-F442 ◽  
Author(s):  
M. Baum ◽  
O. W. Moe ◽  
D. L. Gentry ◽  
R. J. Alpern
Keyword(s):  
Proximal Tubule ◽  
Mammalian Cells ◽  
Brush Border Membrane ◽  
Renal Cortex ◽  
Membrane Vesicles ◽  
Mrna Abundance ◽  
Renal Brush Border Membrane ◽  
Acute Increase ◽  
Glucocorticoid Deficiency ◽  
Convoluted Tubules

Glucocorticoids play an important role in modulating proximal tubule acidification. Chronic systemic administration of dexamethasone increases the rate of bicarbonate absorption in isolated perfused proximal convoluted tubules and Na+/H+ antiporter activity in renal brush-border membrane vesicles. The proximal tubule expresses mRNA corresponding to two known Na+/H+ antiporter isoforms: NHE-3, an amiloride-resistant apical membrane Na+/H+ antiporter; and NHE-1, an amiloride-sensitive Na+/H+ antiporter found on most mammalian cells. Administration of dexamethasone for 1 and 2 days (600 micrograms/kg twice daily and 2 h before animals were killed) increased NHE-3 mRNA abundance 1.3- and 2.5-fold, respectively, but had no effect on NHE-1 mRNA abundance. Aminoglutethimide-induced glucocorticoid deficiency had no effect on NHE-1 or NHE-3 mRNA abundance. Incubation of proximal tubules for 3 h with 10(-5) M dexamethasone increased proximal tubule Na+/H+ antiporter activity from 0.69 +/- 0.04 to 0.92 +/- 0.03 pH units/min (P < 0.01); however, there was no increase in NHE-3 or NHE-1 mRNA abundance. Similarly, there was no effect on NHE-3 or NHE-1 mRNA abundance in rabbit renal cortex 4 h after intravenous administration of 600 micrograms/kg dexamethasone. Thus chronic dexamethasone increases NHE-3 but not NHE-1 mRNA abundance. The acute increase in Na+/H+ antiporter activity induced by dexamethasone occurs by mechanisms independent of changes in NHE-1 and NHE-3 mRNA abundance.

scholarly journals A kinetically defined Na+/H+ antiporter within a mathematical model of the rat proximal tubule.

1995 ◽  
Vol 105 (5) ◽  
pp. 617-641 ◽  
Author(s):  
A M Weinstein
Keyword(s):  
Kinetic Model ◽  
Proximal Tubule ◽  
Membrane Vesicles ◽  
Model Calculations ◽  
Kinetic Formulation ◽  
Luminal Membrane ◽  
Least Squares Fit ◽  
Velocity Effect ◽  
Rat Proximal Tubule

The luminal membrane antiporter of the proximal tubule has been represented using the kinetic formulation of E. Heinz (1978. Mechanics and Engergetics of Biological Transport. Springer-Verlag, Berlin) with the assumption of equilibrium binding and 1:1 stoichiometry. Competitive binding and transport of NH+4 is included within this model. Ion affinities and permeation velocities were selected in a least-squares fit to the kinetic parameters determined experimentally in renal membrane vesicles (Aronson, P.S., M.A. Suhm, and J. Nee. 1983. Journal of Biological Chemistry. 258:6767-6771). The modifier role of internal H+ to enhance transport beyond the expected kinetics (Aronson, P.S., J. Nee, and M. A. Suhm. 1982. Nature. 299:161-163) is represented as a velocity effect of H+ binding to a single site. This kinetic formulation of the Na+/H+ antiporter was incorporated within a model of the rat proximal tubule (Weinstein, A. M. 1994. American Journal of Physiology. 267:F237-F248) as a replacement for the representation by linear nonequilibrium thermodynamics (NET). The membrane density of the antiporter was selected to yield agreement with the rate of tubular Na+ reabsorption. Simulation of 0.5 cm of tubule predicts that the activity of the Na+/H+ antiporter is the most important force for active secretion of ammonia. Model calculations of metabolic acid-base disturbances are performed and comparison is made among antiporter representations (kinetic model, kinetic model without internal modifier, and NET formulation). It is found that the ability to sharply turn off Na+/H+ exchange in cellular alkalosis substantially eliminates the cell volume increase associated with high HCO3- conditions. In the tubule model, diminished Na+/H+ exchange in alkalosis blunts the axial decrease in luminal HCO3- and thus diminishes paracellular reabsorption of Cl-. In this way, the kinetics of the Na+/H+ antiporter could act to enhance distal delivery of Na+, Cl-, and HCO3- in acute metabolic alkalosis.

scholarly journals Prenatal programming of rat proximal tubule Na+/H+ exchanger by dexamethasone

2007 ◽  
Vol 292 (3) ◽  
pp. R1230-R1235 ◽  
Author(s):  
Amit Dagan ◽  
Jyothsna Gattineni ◽  
Vodi Cook ◽  
Michel Baum
Keyword(s):  
Proximal Tubule ◽  
Membrane Vesicles ◽  
Sodium Reabsorption ◽  
Prenatal Programming ◽  
Sprague Dawley ◽  
Sprague Dawley Rats ◽  
Proximal Tubular ◽  
Old Rats ◽  
Convoluted Tubules

Prenatal administration of dexamethasone causes hypertension in rats when they are studied as adults. Although an increase in tubular sodium reabsorption has been postulated to be a factor programming hypertension, this has never been directly demonstrated. The purpose of this study was to examine whether prenatal programming by dexamethasone affected postnatal proximal tubular transport. Pregnant Sprague-Dawley rats were injected with intraperitoneal dexamethasone (0.2 mg/kg) daily for 4 days between the 15th and 18th days of gestation. Prenatal dexamethasone resulted in an elevation in systolic blood pressure when the rats were studied at 7–8 wk of age compared with vehicle-treated controls: 131 ± 3 vs. 115 ± 3 mmHg ( P < 0.001). The rate of proximal convoluted tubule volume absorption, measured using in vitro microperfusion, was 0.61 + 0.07 nl·mm−1·min−1 in control rats and 0.93+ 0.07 nl·mm−1·min−1 in rats that received prenatal dexamethasone ( P < 0.05). Na+/H+ exchanger activity measured in perfused tubules in vitro using the pH-sensitive dye BCECF showed a similar 50% increase in activity in proximal convoluted tubules from rats treated with prenatal dexamethasone. Although there was no change in abundance of NHE3 mRNA, the predominant luminal proximal tubule Na+/H+ exchanger, there was an increase in NHE3 protein abundance on brush-border membrane vesicles in 7- to 8-wk-old rats receiving prenatal dexamethasone. In conclusion, prenatal administration of dexamethasone in rats increases proximal tubule transport when rats are studied at 7–8 wk old, in part by stimulating Na+/H+ exchanger activity. The increase in proximal tubule transport may be a factor mediating the hypertension by prenatal programming with dexamethasone.

scholarly journals Renal miR-148b is associated with megalin down-regulation in IgA nephropathy

2018 ◽  
Vol 38 (6) ◽  
Author(s):  
Lu Wen ◽  
Zhanzheng Zhao ◽  
Jing Xiao ◽  
Zheng Wang ◽  
Xiangfei He ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Mrna Expression ◽  
Iga Nephropathy ◽  
Linear Regression Analysis ◽  
Multiple Linear Regression Analysis ◽  
Mrna Levels ◽  
Immunofluorescence Labeling ◽  
Normal Controls

Megalin is essential for proximal tubule reabsorption of filtered proteins, hormones, and vitamins, and its dysfunction has been reported in IgA nephropathy (IgAN). miR-148b has been shown to regulate renal megalin expression in vitro and in animal models of kidney disease. We examined a potential role of miR-148b and other miRNAs in regulating megalin expression in IgAN by analyzing the association between megalin and miR-148b, miR-21, miR-146a, and miR-192 expression. Quantitative PCR (qPCR) analysis identified a marked increase in renal levels of several miRNAs, including miR-148b, miR-21, miR-146a, and a significant decrease in megalin mRNA levels in IgAN patients when compared with normal controls. By multiple linear regression analysis, however, only renal miR-148b was independently associated with megalin mRNA levels in IgAN. Proximal tubule megalin expression was further evaluated by immunofluorescence labeling of biopsies from the patients. The megalin expression was significantly lower in patients with highest levels of renal miR-148b compared with patients with lowest levels. To examine the direct effects of the miRNAs on megalin and other membrane proteins expression, proximal tubule LLC-PK1 cells were transfected with miR-148b, miR-21, miR-146a, or miR-192 mimics. Transfection with miR-148b mimic, but not the other three miRNA mimics inhibited endogenous megalin mRNA expression. No significant effect of any of the four miRNA mimics was observed on cubilin or aquaporin 1 (AQP1) mRNA expression. The findings suggest that miR-148b negatively regulates megalin expression in IgAN, which may affect renal uptake and metabolism of essential substances.

Renal adaptation to dietary phosphate deprivation: role of proximal tubule brush-border membrane fluidity

1991 ◽  
Vol 260 (5) ◽  
pp. F613-F618 ◽  
Author(s):  
B. S. Levine ◽  
K. A. Knibloe ◽  
K. Golchini ◽  
S. Hashimoto ◽  
I. Kurtz
Keyword(s):  
Proximal Tubule ◽  
Brush Border ◽  
Temporal Relationship ◽  
Brush Border Membrane ◽  
Renal Cortex ◽  
Pi Transport ◽  
Renal Adaptation ◽  
Dietary Phosphate ◽  
Pi Deprivation

With dietary phosphate (Pi) restriction, fluidity of renal proximal tubule brush-border membranes (BBM) and Na-dependent Pi transport (Na-Pi) are increased, suggesting that changes in BBM fluidity are critical for adaptation to Pi restriction. To test this hypothesis, the temporal relationship between Na-Pi transport and changes in BBM fluidity was assessed after Pi deprivation in rats. Renal cortex was obtained from rats fed either a 0.03% (-P) or a 0.6% (+P) Pi diet for 4 h or 7 days, and BBM were prepared. Na-Pi uptake by BBM was measured by use of rapid filtration, and BBM fluidity was assessed by use of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH). After 4 h on the diets, Na-Pi uptake was 439 +/- 142 (SD) and 984 +/- 184 pmol.mg protein-1.5 s-1 in +P and -P, respectively (P less than 0.01, n, = 8). Na-dependent proline uptake was unchanged. DPH anisotropy and total cholesterol were similar between groups: 0.204 +/- 0.025 and 0.401 +/- 0.047 nmol/mg protein, respectively, in +P and 0.205 +/- 0.015 and 0.392 +/- 0.037 in -P (P greater than 0.05, n = 8-10). After 7 days, Na-Pi uptake was 841 +/- 291 in +P and 2,168 +/- 848 pmol.mg protein-1.5 s-1 in -P, P less than 0.01, n = 8. DPH anisotropy and BBM cholesterol were 0.175 +/- 0.019 and 443 +/- 132 nmol/mg protein, respectively, in +P and 0.162 +/- 0.020 (n = 8) and 341 +/- 128 (n = 3) in -P (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

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