Acute hypertension provokes internalization of proximal tubule NHE3 without inhibition of transport activity

2002 ◽  
Vol 282 (4) ◽  
pp. F730-F740 ◽  
Author(s):  
Li Yang ◽  
Patrick K. K. Leong ◽  
Jennifer O. Chen ◽  
Nilem Patel ◽  
Sarah F. Hamm-Alvarez ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Brush Border ◽  
Density Gradient Centrifugation ◽  
Gradient Centrifugation ◽  
Transport Activity ◽  
Sprague Dawley ◽  
Acute Hypertension ◽  
Sprague Dawley Rats ◽  
Cortical Membranes ◽  
Apical Membranes

Acute hypertension rapidly decreases proximal tubule (PT) Na+ reabsorption, facilitated by a redistribution of PT Na+/H+exchangers (NHE3) out of the apical brush border, increasing NaCl at the macula densa, the signal for autoregulation of renal blood flow and GFR. This study aimed to determine whether NHE3 activity per transporter decreases during acute hypertension and the time dependence of the response. Blood pressure was elevated by 50–60 mmHg in male Sprague-Dawley rats for 5 or 30 min by constricting arteries. Renal cortical membranes were fractionated by density gradient centrifugation. NHE3 transport activity was assayed as the rate of appearance of acridine orange (AO) from AO-loaded vesicles in response to an inwardly directed Na+ gradient. After 5-min hypertension, 20% of total NHE3 protein, assayed by immunoblot, redistributed from low-density apical membranes to middensity membranes enriched in intermicrovillar cleft markers; by 30 min, a similar percentage shifted to heavier density membranes containing markers of endosomes. NHE3 activity shifted to higher density membranes along with NHE3 protein, that is, no change in activity/transporter during acute hypertension. Confocal analysis of NHE3 distribution also verified removal from apical microvilli and appearance in subapical vesicles. We conclude that the decrease in renal PT Na+ transport during acute hypertension is mediated by removal of transport-competent NHE3 from the apical brush border to subapical and internal reserves.

Permeability of the microcirculation in area postrema of rat

1988 ◽  
Vol 46 ◽  
pp. 348-349
Author(s):  
Shams M. Ghoneim ◽  
Frank M. Faraci ◽  
Gary L. Baumbach
Keyword(s):  
Brain Stem ◽  
Area Postrema ◽  
Upper Body ◽  
Sprague Dawley ◽  
Sodium Cacodylate ◽  
Acute Hypertension ◽  
Sprague Dawley Rats ◽  
Ultrastructural Characteristics ◽  
The Brain ◽  
Adjacent Brain

The area postrema is a circumventricular organ in the brain stem and is one of the regions in the brain that lacks a fully functional blood-brain barrier. Recently, we found that disruption of the microcirculation during acute hypertension is greater in area postrema than in the adjacent brain stem. In contrast, hyperosmolar disruption of the microcirculation is greater in brain stem. The objective of this study was to compare ultrastructural characteristics of the microcirculation in area postrema and adjacent brain stem.We studied 5 Sprague-Dawley rats. Horseradish peroxidase was injected intravenously and allowed to circulate for 1, 5 or 15 minutes. Following perfusion of the upper body with 2.25% glutaraldehyde in 0.1 M sodium cacodylate, the brain stem was removed, embedded in agar, and chopped into 50-70 μm sections with a TC-Sorvall tissue chopper. Sections of brain stem were incubated for 1 hour in a solution of 3,3' diaminobenzidine tetrahydrochloride (0.05%) in 0.05M Tris buffer with 1% H2O2.

Proximal tubule microvilli remodeling and albuminuria in the Ren2 transgenic rat

2007 ◽  
Vol 292 (2) ◽  
pp. F861-F867 ◽  
Author(s):  
Melvin R. Hayden ◽  
Nazif A. Chowdhury ◽  
Shawna A. Cooper ◽  
Adam Whaley-Connell ◽  
Javad Habibi ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Blood Pressure ◽  
Systolic Blood Pressure ◽  
Proximal Tubule ◽  
Structural Damage ◽  
Kidney Tissue ◽  
Proximal Tubule Cell ◽  
Ang Ii ◽  
Sprague Dawley ◽  
Sprague Dawley Rats

TG(mRen2)27 (Ren2) transgenic rats overexpress the mouse renin gene, with subsequent elevated tissue ANG II, hypertension, and nephropathy. The proximal tubule cell (PTC) is responsible for the reabsorption of 5–8 g of glomerular filtered albumin each day. Excess filtered albumin may contribute to PTC damage and tubulointerstitial disease. This investigation examined the role of ANG II-induced oxidative stress in PTC structural remodeling: whether such changes could be modified with in vivo treatment with ANG type 1 receptor (AT1R) blockade (valsartan) or SOD/catalase mimetic (tempol). Male Ren2 (6–7 wk old) and age-matched Sprague-Dawley rats were treated with valsartan (30 mg/kg), tempol (1 mmol/l), or placebo for 3 wk. Systolic blood pressure, albuminuria, N-acetyl-β-d-glucosaminidase, and kidney tissue malondialdehyde (MDA) were measured, and ×60,000 transmission electron microscopy images were used to assess PTC microvilli structure. There were significant differences in systolic blood pressure, albuminuria, lipid peroxidation (MDA and nitrotyrosine staining), and PTC structure in Ren2 vs. Sprague-Dawley rats (each P < 0.05). Increased mean diameter of PTC microvilli in the placebo-treated Ren2 rats ( P < 0.05) correlated strongly with albuminuria ( r2 = 0.83) and moderately with MDA ( r2 = 0.49), and there was an increase in the ratio of abnormal forms of microvilli in placebo-treated Ren2 rats compared with Sprague-Dawley control rats ( P < 0.05). AT1R blockade, but not tempol treatment, abrogated albuminuria and N-acetyl-β-d-glucosaminidase; both therapies corrected abnormalities in oxidative stress and PTC microvilli remodeling. These data indicate that PTC structural damage in the Ren2 rat is related to the oxidative stress response to ANG II and/or albuminuria.

Abstract 41: Fructose Stimulates Na/H Exchanger 3 Activity and Enhances the Ability of Angiotensin II to Activate Na/H Exchanger 3 in the Proximal Tubule

Hypertension ◽  
2013 ◽  
Vol 62 (suppl_1) ◽  
Author(s):  
Pablo Cabral ◽  
Nancy Hong ◽  
Jeffrey Garvin
Keyword(s):  
Angiotensin Ii ◽  
Proximal Tubule ◽  
Physiological Saline ◽  
Ang Ii ◽  
Sprague Dawley ◽  
Basal Rate ◽  
Low Concentrations ◽  
Sprague Dawley Rats ◽  
High Fructose ◽  
Salt Sensitive Hypertension

Consumption of high-fructose corn syrup as a sweetener has increased dramatically. Fructose has been implicated in the epidemic of diabetes, obesity and hypertension including salt-sensitive hypertension. However, the mechanisms are poorly understood. The proximal nephron reabsorbs 60-70% of the fluid and Na, and most of the filtered bicarbonate via Na/H exchanger 3. Enhanced proximal nephron transport has been implicated in several forms of hypertension. We hypothesized that fructose stimulates NHE3 activity and enhances the ability of angiotensin II (ANG II) to activate NHE3 in the proximal tubule. To test our hypothesis we isolated and perfused proximal tubules from Sprague Dawley rats. NHE3 activity was measured as the recovery of intracellular pH after an NH4Cl acid pulse using the pH sensitive dye BCECF. The rate of pH recovery was measured in Fluorescent Units per second (FU/sec). In the presence of a 5.5 mM glucose-containing physiological saline the basal rate of pH recovery was 3.1 ± 0.8 FU/sec. When the luminal solution was exchanged to a 0.6 mM glucose + 5 mM fructose-containing physiological saline in a second period, the rate of pH recovery increased to 5 ± 1 FU/sec (p<0.03, n=8).To study whether this effect was due to the addition of fructose or the removal of glucose to the lumen, we performed a separate set of experiments where 5 mM glucose was substituted for 5 mM fructose. In the presence of 0.6 mM glucose the basal rate of pH recovery was 3.6 ± 1.5 FU/sec. When 5 mM fructose was added the rate of pH recovery increased to 5.9 ± 2 FU/sec (p<0.02, n=5). Control experiments showed no differences between periods when 5 mm glucose was added back to the luminal perfusate. Finally, we tested the effect of low concentrations of ANG II in the presence or absence of luminal fructose. In the presence of 5.5 mM glucose, ANG II 10-12 M did not affect the rate of pH recovery (change: -1.1 ± 0.5 FU/sec, n=9). However, in the presence of 5 mM fructose, ANG II increased the rate of pH recovery (change: 4.0 ± 2.2 FU/sec, p< 0.03 n=6). We conclude that acute treatment with fructose stimulates NHE3 activity and enhances the ability of ANG II to activate NHE3 in the proximal tubule. These results may partially explain the mechanism by which a fructose diet induces hypertension.

Mechanism underlying diuretic effect of l-NAME at a subpressor dose

2001 ◽  
Vol 281 (3) ◽  
pp. F414-F419 ◽  
Author(s):  
Mingyu Liang ◽  
Theresa J. Berndt ◽  
Franklyn G. Knox
Keyword(s):  
Proximal Tubule ◽  
Flow Rate ◽  
Nitrate Concentration ◽  
Distal Tubule ◽  
No Synthase ◽  
Urine Flow ◽  
Sprague Dawley ◽  
Sprague Dawley Rats ◽  
Renal Tubular ◽  
Nitrite Nitrate

The diuretic effects of nitric oxide (NO) synthase inhibitors administered at subpressor dose in rats are controversial, and the tubular segments involved are not known. In the present study, we examined the effect of N ω-nitro-l-arginine methyl ester (l-NAME) at a subpressor dose on renal interstitial NO and cGMP activity and on renal tubular segmental reabsorption of fluid in the rat. Intravenous infusion of l-NAME at 1 μg · kg−1 · min−1 in Sprague-Dawley rats ( N = 8), which did not alter mean arterial pressure or glomerular filtration rate, significantly increased urine flow rate (Uv; from 78.2 ± 12.7 to 117.1 ± 14.9 μl/min, P < 0.05). Paradoxically, this effect of l-NAME was concomitant with significant increases in nitrite/nitrate (from 10.79 ± 1.20 to 16.50 ± 2.60 μM, P < 0.05) and cGMP (from 0.65 ± 0.09 to 0.98 ± 0.18 nM, P < 0.05) concentrations in renal cortical microdialysate as well as the nitrite/nitrate concentration in the medullary microdialysate. Micropuncture studies in the superficial nephron revealed that l-NAME significantly increased the flow rate (from 8.3 ± 0.9 to 12.2 ± 1.2 nl/min, P < 0.05) and fractional delivery of fluid to the distal tubule, but not those in the late proximal tubule. In conclusion, l-NAME, at the subpressor dose used in this study, increased renal nitrate/nitrite and cGMP and inhibited fluid reabsorption in tubular segments between the late proximal tubule and the distal tubule of superficial nephrons.

Permeability of blood-brain barrier to various sized molecules

1985 ◽  
Vol 248 (5) ◽  
pp. H712-H718 ◽  
Author(s):  
W. G. Mayhan ◽  
D. D. Heistad
Keyword(s):  
Blood Brain Barrier ◽  
Fluorescent Microscopy ◽  
Brain Barrier ◽  
Sprague Dawley ◽  
Acute Hypertension ◽  
Size Dependent ◽  
Blood Brain ◽  
Sprague Dawley Rats ◽  
Intravital Fluorescent Microscopy ◽  
Dextran Clearance

We studied disruption of the blood-brain barrier (BBB) by acute hypertension and a hyperosmolar solution. The goals were to determine whether 1) disruption of the BBB occurs primarily in arteries, capillaries, or veins, and 2) transport of different-sized molecules is homogeneous or size dependent. Sprague-Dawley rats were studied using intravital fluorescent microscopy of pial vessels and fluorescein-labeled dextrans (FITC-dextran, mol wt = 70,000, 20,000, and 4,000 daltons). The site of disruption was determined by the appearance of microvascular leaky sites. Transport of different-sized molecules was calculated from clearance of FITC-dextran. During gradual hypertension and osmotic disruption, all leaky sites were venular. Rapid hypertension produced venular leaky sites and, in some experiments, diffuse arteriolar extravasation of FITC-dextran. Clearance of different-sized molecules was homogeneous during acute hypertension. In contrast, clearance of molecules during osmotic disruption was size dependent. The findings suggest that 1) venules and veins are the primary sites of disruption following acute hypertension and a hyperosmolar solution; 2) transport of different-sized molecules is homogeneous following acute hypertension, which suggests a vesicular mechanism; and 3) transport following hyperosmolar disruption is size dependent, which suggests that hyperosmolar disruption may involve formation of pores as well as vesicular transport.

scholarly journals Active Sugar Transport by the Small Intestine

1968 ◽  
Vol 52 (3) ◽  
pp. 482-494 ◽  
Author(s):  
Robert G. Faust ◽  
Mary G. Leadbetter ◽  
Regina K. Plenge ◽  
Alston J. McCaslin
Keyword(s):  
Small Intestine ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Density Gradient Centrifugation ◽  
Gradient Centrifugation ◽  
Sugar Transport ◽  
Initial Step ◽  
Inhibitory Effect ◽  
Glucose Binding ◽  
Brush Borders

Tris-disrupted and intact brush border membrane preparations from mucosa of hamster jejunum were capable of preferentially binding actively transported D-glucose in a similar manner. Density gradient centrifugation of the Tris-disrupted brush borders indicated that D-glucose was bound to a fraction containing the cores or inner material of the microvilli. The properties of this binding were examined with the Tris-disrupted brush border preparation. Actively transported sugars competitively inhibited preferential D-glucose binding, whereas no effect was observed with nonactively transported sugars. Neither actively nor nonactively transported amino acids affected D-glucose binding. D-Glucosamine, which is not actively transported, was inhibitory to preferential D-glucose binding as well as to the active transport of D-glucose by everted sacs of hamster jejunum. No inhibitory effect was observed with the same concentration of D-galactosamine. Preferential D-glucose binding was also inhibited by sulfhydryl-reacting compounds, Ca2+, and Li+ ions. On the other hand, Mg2+ was shown to be stimulatory and Na+, NH4+, and K+ had no effect on this phenomenon. The results of these experiments suggest that preferential D-glucose binding to brush borders is related to the initial step in active sugar transport by the small intestine.

Subcellular Localization of Enterokinase in Human Duodenal Mucosa

1977 ◽  
Vol 53 (6) ◽  
pp. 551-562 ◽  
Author(s):  
R. W. Lobley ◽  
Ruth Franks ◽  
R. Holmes
Keyword(s):  
Brush Border ◽  
Soluble Fraction ◽  
Density Gradient Centrifugation ◽  
Sucrose Solution ◽  
Gradient Centrifugation ◽  
Total Activity ◽  
Duodenal Mucosa ◽  
Differential Centrifugation ◽  
Marker Enzymes ◽  
Suitable Marker

1. Specimens of human duodenal mucosa were obtained at duodenotomy. Superficial mucosal scrapings were homogenized in isotonic sucrose solution and fractionated by differential centrifugation. The distribution of organelles among the subcellular fractions was monitored by assay of suitable marker enzymes. 2. Enterokinase was recovered predominantly in the nuclear + brush-border fraction and 80% of the total activity was found to be particulate; approximately 20% of the enzyme was present in the soluble fraction, compared with 1% of the brush-border markers sucrase and alkaline phosphatase. 3. The brush-border-containing fraction was subfractionated by treatment with hypertonic Tris followed by differential and density gradient centrifugation. Enterokinase was distributed among the subfractions in parallel with brush-border markers and was concentrated in a subfraction which was highly enriched in microvillous membranes. 4. It was concluded that enterokinase is localized primarily to the microvillous membrane of the epithelial cell brush border in man, but that in addition a proportion of the enzyme may be present in a soluble or easily released form in the duodenal mucosa.

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 Maturation of the Na+/H+ antiporter (NHE3) in the proximal tubule of the hypothyroid adrenalectomized rat

2004 ◽  
Vol 287 (3) ◽  
pp. F521-F527 ◽  
Author(s):  
Neena Gupta ◽  
Vangipuram Dwarakanath ◽  
Michel Baum
Keyword(s):  
Proximal Tubule ◽  
Brush Border Membrane ◽  
Mrna Abundance ◽  
Protein Abundance ◽  
Sprague Dawley ◽  
Sham Control ◽  
Sprague Dawley Rats ◽  
Sodium Dependent ◽  
Combined Deficiency

In previous studies examining the role of glucocorticoids and thyroid hormone on the maturation of the Na+/H+ antiporter (NHE3), we found attenuation in the maturational increase in proximal tubule apical Na+/H+ antiporter activity but no change in NHE3 mRNA abundance in either glucocorticoid-deficient or hypothyroid rats. In addition, prevention of the maturational increase in either hormone failed to totally prevent the maturational increase in Na+/H+ antiporter activity. We hypothesized that one hormone played a compensatory role when the other was deficient. The present study examined whether combined deficiency of thyroid and glucocorticoid hormones would completely prevent the maturation of the Na+/H+ antiporter. Adrenalectomy was performed in 9-day-old hypothyroid Sprague-Dawley rats, a time before the normal postnatal maturational increase in these hormones occurs. Nine- and 30-day-old adrenalectomized (ADX), hypothyroid rats had comparable NHE3 mRNA abundance, which was 5- to 10-fold less than 30-day-old ADX, hypothyroid rats that received corticosterone-thyroxine replacement and 30-day-old sham control rats ( P < 0.05). Brush-border membrane NHE3 protein abundance was comparable in 9- and 30-day-old ADX, hypothyroid groups and ∼20-fold lower than both the 30-day replacement and 30-day sham groups ( P < 0.05). Similarly, the replacement and sham groups had higher sodium-dependent proton secretion than 9- and 30-day-old ADX, hypothyroid groups ( P < 0.05). We conclude that combined deficiency of both hormones totally prevents the maturational increase in NHE3 mRNA and protein abundance and Na+/H+ antiporter activity.

Immunocytochemical localization of a brush border hydrolase, lactase, in newborn suckling rat jejunum

1993 ◽  
Vol 51 ◽  
pp. 42-43
Author(s):  
László G. Kömüves ◽  
Mary A. Dudley ◽  
Buford L. Nichols
Keyword(s):  
Brush Border ◽  
Secretory Pathway ◽  
Calf Serum ◽  
Ultrastructural Localization ◽  
Sprague Dawley ◽  
Rat Pups ◽  
Sprague Dawley Rats ◽  
Intracellular Compartments ◽  
Small Intestinal ◽  
Coated Carbon

Lactase-phlorizin hydrolase (LPH, EC 3.2.1.23), an integral membrane glycoprotein of the small intestinal brush border, converts lactose, the main carbohydrate in milk, to its monosaccharide components. Although the activity of LPH is high in suckling rats, little is known about its distribution within the intracellular compartments of the secretory pathway and brush border. We present the first description of the ultrastructural localization of LPH in the neonatal jejunum of suckling rat pups.Pieces of jejunum from 12- to 14-d-old suckling rat pups from three litters of Sprague- Dawley rats were fixed with 4% freshly prepared paraformaldehyde in 100 mM phosphate buffer, pH=7.40, for 4 h, and stored in 1% paraformaldehyde, at 4°C, until further processing. The samples were sectioned after cryoprotection in 2.3 M sucrose in an RMC MT-7 ultramicrotome equipped with CR21 cryoattachment. Ultrathin cryosections were collected on Formvar-coated, carbon-evaporated nickel grids. The nonspecific binding sites were blocked by 1% heat-inactivated newborn calf serum in 10 mM Trizma buffer, pH=7.60, containing 500 mM NaCl, 0.05% NaN3 and 20 mM glycine (buffer A).

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