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PubMed1996

Impaired response to furosemide in hyperprostaglandin E syndrome: evidence for a tubular defect in the loop of Henle.

In hyperprostaglandin E syndrome (HPS) renal wasting of electrolytes and water is consistently associated with enhanced synthesis of prostaglandin E2. In contrast to Bartter or Gitelman syndrome (BS/GS), HPS is characterized by its severe prenatal manifestation, leading to fetal polyuria, development of polyhydramnios, and premature birth. This disorder mimics furosemide treatment with hypokalemic alkalosis, hypochloremia, isosthenuria, and impaired renal conservation of both calcium and magnesium. Therefore the thick ascending limb of the loop of Henle seems to be involved in HPS. To characterize the tubular defect we investigated the response to furosemide (2 mg/kg) in HPS (n = 8) and BS/GS (n = 3) 1 week after discontinuation of long-term indomethacin treatment. Sensitivity to furosemide was completely maintained in patients with BS/GS. The diuretic, saluretic, and hormonal responses were similar to those of a control group of healthy children (n = 13), indicating an intact function of the thick ascending limb of the loop of Henle in BS/GS. In contrast, patients with HPS had a marked resistance to this loop diuretic. Furosemide treatment increased urine output by 7.5 +/- 0.7 ml/kg per hour in healthy control subjects but only by 4.4 +/- 1.2 ml/kg per hour (p < 0.5) in children with HPS. In parallel, the latter also had a markedly impaired saluretic response (delta Cl(urine) 0.14 +/- 0.04 mmol/kg per hour vs 0.85 +/- 0.09 mmol/kg per hour, p < 0.001; delta Na(urine) 0.23 +/- 0.06 mmol/kg per hour vs 0.77 +/- 0.09 mmol/kg per hour, p < 0.001). Furosemide therapy further enhanced prostaglandin E2 excretion in patients with HPS (54 +/- 17 to 107 +/- 28 ng/hr per 1.73 m2, p < 0.05), whereas no significant effect was observed in healthy children (20 +/- 3 to 12 +/- 3 ng/hr per 1.73 m2). We conclude that a defect of electrolyte reabsorption in the thick ascending limb of the loop of Henle plays a major role in HPS.

Bartter Syndrome↗
PubMed1975

Mechanism of NaCl reabsorption by hamster thin ascending limbs of Henle's loop.

Two models of ypertonic urine formation in the inner medulla were tested. The active model asserts that thin ascending limbs of Henle's loop (ALH) reasorb NaCl hypertonically by active transport; the passive model suggests the reabsorption is by diffusion down a concentration gradient. Using (Na+) in ascending vasa recta (AVR) as a measure of interstitial (Na+), we found no concentration difference between loop tubular fluid and AVR, when the comparison was made at the bend of the loop, or at an ALH sampling site 1 mm from the bend; the results were the same in antidiuresis and saline diuresis. In saline diuresis with flow of tubular fluid to the ALH slowed by simultaneous collection at the bend of the loop,ALH (Na+) fell below AVR levels, a result consistent with active transport, but not with a purely passive mechanism. Although contragradient transport was shown only with flow slowed and the corticomedullary gradient reduced, a model suggests the active component contributes almost half the observed Na+ flux in antidiuresis.

Animals↗
PubMed2000

Mixed descending- and ascending-type thin limbs of Henle's loop in mammalian renal inner medulla.

Previous studies have generally indicated that the entire descending (DTL) and ascending thin limbs (ATL) of Henle's loops in the mammalian inner medulla exhibit structurally and functionally distinct properties. In the present study, we found that about 50% of Munich-Wistar rat inner medullary thin limbs, lying at positions distinctly above the bend, had segments exhibiting structural characteristics of DTL located immediately adjacent to segments exhibiting structural characteristics of ATL. Multiple DTL-type and ATL-type segments of variable length existed along a single straight portion of these mixed tubules. Inner medullary thin limbs with repeating, sequential expression of DTL-type and ATL-type regions were also numerous in Sprague-Dawley rats, mice, and rabbits with no evidence of sexual dimorphism. RT-PCR of microdissected segments showed that the water channel aquaporin-1 (AQP1) and the urea transporter UT-A2 were expressed in pure DTL, but not in pure ATL, and in DTL-type, but not in ATL-type, regions of mixed-type thin limbs. Immunocytochemistry revealed expression of AQP1 in cells of pure DTL, but not pure ATL, and in cells of DTL-type, but not ATL-type, regions of mixed-type thin limbs. In contrast, the chloride channel ClC-K1 was expressed in pure ATL, but not pure DTL, and in ATL-type, but not DTL-type, regions of mixed-type thin limbs. Discontinuous axial expression of AQP1, UT-A2, and ClC-K1 along the straight portion of single thin limbs indicates that these nephrons possess a more heterogeneous structure than previously recognized.

Animals↗
PubMedDate not supplied

Cellular adenosine triphosphate production and consumption in the descending thin limb of Henle's loop in the rat.

To characterize the properties of cellular adenosine triphosphate (ATP) production and consumption in the descending thin limb of Henle's loop (DTL) in rats, we measured the cellular ATP content by applying the microchemiluminescence method. For ATP production, isolated DTL from the short- and long-loop nephron (SDL and LDL, respectively) was incubated with several substrates such as alanine, glucose, glutamine, beta-hydroxybutyrate (beta-HBA), lactate, and pyruvate; for ATP production from each substrate indicated that glucose and pyruvate were the preferred substrates to maintain cellular ATP in both SDL and LDL. ATP production from glutamine, beta-HBA, and lactate was substantial in LDL. In SDL, glutamine was the preferred substrate, and beta-HBA and lactate were minimal. The utilization of alanine was minimal in both LDL and SDL. The cellular ATP was significantly restored by ouabain at concentrations of 1.5 x 10(-5) and 1.5 x 10(-3) M in LDL, but in SDL only at 1.5 x 10(-3) M. In both segments, the cellular ATP level was significantly decreased by monensin above the concentrations of 1 micrograms/ml in LDL and 5 micrograms/ml in SDL. From these observations, we conclude that there exist clear differences between LDL and SDL in ATP-supplying substrate specificities and ATP-consuming properties.

Adenosine Triphosphate↗
PubMed1993

Direct evidence for the absence of active Na+ reabsorption in hamster ascending thin limb of Henle's loop.

The mechanisms of Na+ transport across cell membranes were investigated in the in vitro microperfused hamster ascending thin limb (ATL) of Henle's loop using a fluorescent Na+ indicator sodium-binding benzofuran isophthalate. The intracellular Na+ concentration ([Na+]i) of the ATL cells was 17.1 +/- 1.7 mM (n = 22) when the ATL was microperfused in vitro with Hepes-buffered solution containing 204 mM Na+. Elimination of metabolites such as glucose and alanine from the basolateral solution increased [Na+]i. Applying either 5 mM cyanide or 5 mM iodoacetic acid to the bath also increased [Na+]i. The elimination of K+ and the addition of 10(-4) M ouabain in the bath increased [Na+]i by 25.0 +/- 5.0 mM (n = 5) in 3 min and by 10.7 +/- 2.4 mM (n = 4), respectively. The elimination of luminal and basolateral Na+ resulted in a decrease in [Na+]i, indicating Na+ permeability of both the luminal and basolateral cell membranes. The luminal Na+ permeability was not affected by furosemide. The presence of luminal Na+ permeability and the basolateral Na+/K+ ATPase suggests the presence of net active reabsorption of Na+, which is not a physiologically important amount, in our estimation.

Alanine↗
PubMed1995

Structure of the glomerular capillaries of the domestic chicken and desert quail.

The glomerular capillary architecture of nephrons that include a loop of Henle (looped) and those that lack the loop (loopless) nephrons was examined qualitatively and quantitatively by electron microscopy in Gallus gallus and Callipepla gambelii. The glomerular capillaries of looped nephrons form a dichotomously branched network, while those of loopless nephrons are arranged loosely, and the majority are unbranched. There was no significant difference in the diameter of the glomerular capillaries between looped and loopless nephrons; however, in all cases the diameter of the afferent arteriole was significantly larger than that of the efferent arteriole. Based on size alone, the predicted blood flow rate in the efferent arteriole is 20% that of the afferent arteriole in G.gallus and 7% that of the afferent arteriole in C.gambelii. There was no significant difference in the volume density (Vv) of the glomerular capillaries between looped and loopless nephrons. However, the surface area density (Sv) of the glomerular capillaries in loopless nephrons of C.gambelii was significantly larger than for the looped nephrons, and for the loopless nephrons in G. gallus. This suggests that there may be a decrease in blood flow rate along the glomerular capillaries of the loopless nephrons in C. gambelii. Overall, the results indicate that the avian glomerular capillaries are less complex than those of mammals.

Animals↗
PubMed1987

Functional heterogeneity in the hamster medullary thick ascending limb of Henle's loop.

Cellular heterogeneity was examined in the hamster medullary thick ascending limb (MAL) perfused in vitro by electrophysiological measurements with an intracellular microelectrode. Random measurements of fractional resistance of basolateral membrane (RfB) revealed two cell populations, high basolateral conductance (HBC) cells having RfB of 0.05 +/- 0.01 (n = 24) and low basolateral conductance (LBC) cells having RfB of 0.80 +/- 0.03 (n = 32). Basolateral membrane potentials (VB) were not different between HBC cells and LBC cells (-72.6 +/- 1.2, n = 43 vs. -70.0 +/- 1.2, n = 35). Addition of 2 mmol/l Ba2+ to the bath depolarized the basolateral membrane in the HBC cells from -70.4 +/- 3.2 to -20.9 +/- 5.9 mV (n = 8) but not in the LBC cells (from -74.4 +/- 1.9 to -72.0 +/- 2.1 mV). Increasing K+ or decreasing Cl- in the bathing solution caused marked positive deflection of VB in the HBC cells but little or no change in VB in the LBC cells. Elimination of Cl- from the lumen or addition of furosemide to the lumen enhanced the potential response of the HBC cells to basolateral application of Ba2+. Accordingly, with Ba2+ present in the bath, the potential response of the HBC cells to a decrease in bath Cl- concentration was enhanced. These observations suggest that a K+ conductance exists in the basolateral membrane of HBC cells in parallel with a Cl- conductance. The basolateral cell membrane of LBC cells also contains a Cl- conductance.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Effects of solute concentration on vasopressin stimulated cyclic AMP generation in the rat medullary thick ascending limbs of Henle's loop.

We examined effects of osmolality or sodium concentration on vasopressin induced cyclic AMP generation in the medullary thick ascending limbs isolated from collagenase treated rat kidneys. Vasopressin-stimulated cyclic AMP generation was increased as a function of NaCl concentration of the incubation medium. Addition of sucrose was also effective in enhancing the vasopressin-stimulated cyclic AMP, whereas addition of urea was without effect. When incubation medium was made hypertonic with sodium cyclamate, vasopressin-stimulated cyclic AMP generation was also enhanced. When choline chloride was used instead of sodium cyclamate, only an insignificant increase in the hormone-stimulated cyclic AMP generation was observed. These results suggest that the responsiveness of the rat medullary thick ascending limbs to vasopressin is regulated, at least in part, by transmembrane osmotic gradient.

Animals↗
PubMed2000

A simple method for obtaining functionally and morphologically intact primary cultures of the medullary thick ascending limb of Henle's loop (MTAL) from rabbit kidneys.

We describe a simple method for obtaining functionally and morphologically intact primary cultures of cells from the medullary thick ascending limb of rabbit kidneys. After digesting dissected fragments of the inner stripe of the outer medulla with collagenase, a suspension of tubule fragments is obtained, the vast majority of which are medullary thick ascending limb (MTAL) segments. These are identified individually by their morphological appearance and large amounts are collected with a micropipette mounted on a micromanipulator. This ensures maximal homogeneity of the starting material. Monolayers of cells grow out of these MTAL segments after seeding them onto collagen-coated, permeable filter supports. During the week following confluence, the cultures exhibit an apical side-positive transepithelial potential difference. Electron microscopic examination shows a monolayer of polarised cells with characteristics of distal tubular cells. The primary cultures express Tamm-Horsfall protein at their apical surface. Additional evidence for their differentiation and polarisation is the net ammonium influx, which occurs at very high rates across the apical membrane and is much slower across the basolateral membrane, as judged by measurements of intracellular pH. Adenosine 3',5'-cyclic monophosphate (cAMP) production is stimulated by arginine-vasopressin, calcitonin or isoproterenol (all 1 micromol/l). Intracellular calcium signalling is observed after stimulation with 1 micromol/l adenosine, adenosine 5'-triphosphate (ATP) and bradykinin. In addition, we compared these characteristics with those of TALH-SVE cell monolayers, an established immortalised cell line of the same origin.

1-Methyl-3-isobutylxanthine↗
PubMed2000

Cellular adaptation of the mouse cortical thick ascending limb of Henle's loop (CTAL) to dietary magnesium restriction: enhanced transepithelial Mg2+ and Ca2+ transport.

Mice aged 4 or 8 weeks were fed with a low-Mg2+ diet for 1, 2, 3 or 4 days. After 1 day of diet, the urinary excretion of Mg2+ and Ca2+ was strongly reduced in both animal groups (4 and 8 weeks), accompanied by a significant fall in plasma Mg2+ concentration and an increase in urinary volume. This profile persisted after 2, 3 or 4 days of dietary Mg2+ restriction. After 1 day of diet, transepithelial ion net fluxes of Na+, Cl-, Ca2+ and Mg2+ (JNa' JCI, JCl, JMg) measured in vitro from isolated perfused cortical thick ascending limbs (CTALs) of these animals remained unchanged. After 2 days of diet, measurements of J(Ca) and J(Mg) in isolated perfused CTALs showed that transepithelial Mg2+ and Ca2+ reabsorption were enhanced in CTALs from Mg(2+)-depleted, 8-week-old animals, whereas transepithelial Mg2+ and Ca2+ transport were not altered in 4-week-old mice. JNa and JCl and the transepithelial potential (PDte) were not modified in CTALs from either animal group. Our results suggest that a low-Mg2+ diet leads to urinary retention of Mg2+ and Ca2+ which is most likely due to increased Mg2+ and Ca2+ transport in the CTAL. Furthermore, in response to dietary Mg2+ restriction, the reabsorption of divalent cations in the CTAL of adult, but not of young, mice undergoes cellular adaptation.

Adaptation, Physiological↗
PubMed1991

A mathematical model of rabbit cortical thick ascending limb of the Henle's loop.

A mathematical version of the cell model of the cortical thick ascending limb of the rabbit proposed by Greger and Schlatter ((1983) Pfügers Arch. 396, 325-334) is described. Available data are sufficient to compute the most important parameters. Simulations of experiments with perfused tubules in which the transepithelial voltage and conductance, and the intracellular electrical potential were measured in the course of ionic substitutions in the perfusing baths or treatment with ouabain or furosemide are in good agreement with the experimental results with the exception of those relating to dilution potential experiments. The model can be used in the analysis and planning of experiments and is capable of predicting the instantaneous values of ionic fluxes and intracellular concentrations and of cell volume.

Animals↗