Sodium-dependent net urea transport in rat initial inner medullary collecting ducts.

Isozaki, Taisuke; Lea, Janice P.; Tumlin, James A.; Sands, Jeff M.

doi:10.1172/jci117491

Cited by 57 publications

(52 citation statements)

References 25 publications

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“…Schmidt-Nielsen and colleagues first demonstrated the existence of active urea reabsorption which is coupled to sodium reabsorption in the kidney of the spiny dogfish, Squalus acanthias (16). We showed that urea is actively reabsorbed via a secondary active, sodium-coupled cotransport process in the rat initial IMCD (IMCD 1 ) from rats fed a low-protein diet for 3 wk (9)(10)(11). We also showed that urea is actively secreted via a secondary active, sodium-coupled countertransport process in the deepest portion of the rat terminal IMCD, the IMCD 3 , but not in the middle third of the IMCD, the IMCD 2 , nor in the initial IMCD of rats fed a normal diet (12).…”

Section: Introductionmentioning

confidence: 94%

“…Tubules were transferred into a bath that was continuously exchanged and bubbled with 95% O 2 /5% CO 2 gas and perfused using standard techniques (10,12,20).…”

Section: Protocolsmentioning

confidence: 99%

“…In addition to facilitated urea transport, there is evidence for active urea transport process(es) in the kidney of rat (9)(10)(11)(12), rabbit (13), dog (14,15), spiny dogfish (16), and human (17). Schmidt-Nielsen and colleagues first demonstrated the existence of active urea reabsorption which is coupled to sodium reabsorption in the kidney of the spiny dogfish, Squalus acanthias (16).…”

Section: Introductionmentioning

confidence: 99%

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Active sodium-urea counter-transport is inducible in the basolateral membrane of rat renal initial inner medullary collecting ducts.

Kato¹,

Sands²

1998

J. Clin. Invest.

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Rat inner medullary collecting ducts (IMCD 3 s) possess a luminal Na ϩ -dependent, active urea secretory transport process, which is upregulated by water diuresis. In this study of perfused IMCDs microdissected from base (IMCD 1 ), middle (IMCD 2 ), or tip (IMCD 3 ) of the inner medulla, we tested whether furosemide diuresis alters active urea transport. Rats received furosemide (10 mg/d s.c. for 3-4 d) and were compared with pair-fed control rats. Furosemide significantly decreased urine osmolality and urea clearance, and increased blood urea nitrogen. IMCD 3 s from furosemidetreated rats had significantly lower rates of active urea secretion than IMCD 3 s from control rats. IMCD 2 s showed no active urea transport in control or furosemide-treated rats.

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Section: Introductionmentioning

confidence: 94%

“…Tubules were transferred into a bath that was continuously exchanged and bubbled with 95% O 2 /5% CO 2 gas and perfused using standard techniques (10,12,20).…”

Section: Protocolsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Active sodium-urea counter-transport is inducible in the basolateral membrane of rat renal initial inner medullary collecting ducts.

Kato¹,

Sands²

1998

J. Clin. Invest.

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“…The higher urea permeability in the adult BBMV could be due to maturational increases of other urea transporters such as the sodium-dependent urea transporter that has been recently described (14,15) . To assess the sodium dependence of urea transport in the proximal tubule apical membrane, urea uptake was measured in the presence and absence of a 20-mM sodium gradient in adult BBMV.…”

Section: Sodium Dependence Of Bbmv Urea Transportmentioning

confidence: 95%

Maturational Changes in Rabbit Renal Brush Border Membrane Vesicle Urea Permeability • 1830

Quigley¹,

Flynn²,

Baum³

1998

Pediatr Res

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Urea transport in the proximal tubule is thought to occur by passive diffusion through the lipid bilayers of the cell membranes. The lipid composition of cell membranes changes during maturation and may directly affect urea permeability of proximal tubule membranes. The present study examined the maturation of urea transport in rabbit renal brush border membrane vesicles (BBMV). BBMV from adult and neonatal (9-to 11-d-old) New Zealand white rabbits were loaded with 500 mM urea and mixed with an iso-osmotic mannitol solution using a stop-flow instrument. Vesicle shrinkage, due to efflux of urea, was followed with light scattering and urea permeability was calculated from an exponential fit of the data. Urea permeability was significantly lower in the neonatal BBMV than the adult at 25°C (0.34 ± 0.04 × 10 −6 versus 0.56 ± 0.03 × 10 −6 cm/sec; p < 0.001, n = 7) and 37°C (0.45 ± 0.04 × 10 −6 versus 0.66 ± 0.03 × 10 −6 cm/sec; p = 0.001, n = 7). There was no effect of 250 µM phloretin on urea permeability in either adult or neonatal BBMV at either temperature. The activation energy for urea diffusion was higher in the neonatal than the adult BBMV. Because the maturational increase in urea permeability could potentially be due to a sodium-dependent urea transporter in the adult BBMV, the sodium dependence of urea uptake in adult BBMV was examined. There was no difference in urea permeability in the presence or absence of 20 mM NaCl. Permeability of the lipid-soluble molecule, glycerol, was also found to be the same in the neonatal and adult BBMV. Urea transport in the apical membrane of neonatal and adult proximal tubules is not phloretin sensitive, a finding consistent with diffusion of urea via the lipid bilayer. The rate of urea diffusion is lower in neonatal membranes and may be an important factor in overall urea excretion. This may also play a role in developing and maintaining a high medullary urea concentration and thus the ability to concentrate the urine during renal maturation.In most mammals, nitrogen waste from metabolism of amino acids is excreted in the urine as urea (1,2) . The proximal tubule reabsorbs approximately 50% of the filtered load of urea despite changes in hydration status and protein intake that alter the overall excretion of urea. Although initial studies suggested that the proximal straight tubule actively secreted urea ( and that membrane transport of urea in the proximal tubule may occur by a specific transporter (4) , most evidence indicates that urea transport in the proximal tubule occurs by passive diffusion through the lipid bilayer (1,2) . The phospholipid composition of membranes has a direct influence on solute permeabilities and thus may directly affect proximal tubule transport of urea (5) .During maturation, the proximal tubule of the rabbit is known to undergo many changes in active and passive transport characteristics (6,7) . The lipid composition of brush border membranes also changes during development and may play a role in the maturation of transport processes...

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“…UT-A) and secondary active Na + /urea counter-transport systems (Chou and Knepper, 1989;Isozaki et al, 1993;Isozaki et al, 1994a;Isozaki et al, 1994b;Sands et al, 1996;Kato and Sands, 1998a;Kato and Sands, 1998b), but not Na + /urea cotransporters, and because water with a salinity of 1 contained ~15mmoll -1 Na + , which was higher than the normal intracellular Na + concentration (10mmoll -1 ), the possibility of a Na + /urea counter-transporter being expressed in the apical membrane of the buccopharyngeal epithelial cells of P. sinensis cannot be eliminated at present. However, active buccopharyngeal urea excretion resulted in extraordinarily high urea concentrations (~614mmoll -1 ) in the saliva of turtles injected intraperitoneally with urea; therefore, the possibility of the presence of a novel active urea transporter independent of Na + movement in the apical surface of the buccopharyngeal epithelium cannot be ignored.…”

Section: The Buccopharyngeal Epithelium Is Capable Of Active Urea Excmentioning

confidence: 97%

The Chinese soft-shelled turtle,Pelodiscus sinensis, excretes urea mainly through the mouth instead of the kidney

Loong

Lee

et al. 2012

Journal of Experimental Biology

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SUMMARY The Chinese soft-shelled turtle, Pelodiscus sinensis, is well adapted to aquatic environments, including brackish swamps and marshes. It is ureotelic, and occasionally submerges its head into puddles of water during emersion, presumably for buccopharyngeal respiration. This study was undertaken to test the hypothesis that the buccophyaryngeal cavity constitutes an important excretory route for urea in P. sinensis. Results indicate that a major portion of urea was excreted through the mouth instead of the kidney during immersion. When restrained on land, P. sinensis occasionally submerged their head into water (20–100 min), during which urea excretion and oxygen extraction occurred simultaneously. These results indicate for the first time that buccopharyngeal villiform processes (BVP) and rhythmic pharyngeal movements were involved in urea excretion in P. sinensis. Urea excretion through the mouth was sensitive to phloretin inhibition, indicating the involvement of urea transporters (UTs). In addition, saliva samples collected from the buccopharyngeal surfaces of P. sinensis injected intraperitoneally with saline contained ~36 mmol N l−1 urea, significantly higher than that (~2.4 mmol N l−1) in the plasma. After intraperitoneal injection with 20 μmol urea g−1 turtle, the concentration of urea in the saliva collected from the BVP increased to an extraordinarily high level of ~614 μmol N ml−1, but the urea concentration (~45 μmol N ml−1) in the plasma was much lower, indicating that the buccopharyngeal epithelium of P. sinensis was capable of active urea transport. Subsequently, we obtained from the buccopharyngeal epithelium of P. sinensis the full cDNA sequence of a putative UT, whose deduced amino acid sequence had ~70% similarity with human and mouse UT-A2. This UT was not expressed in the kidney, corroborating the proposition that the kidney had only a minor role in urea excretion in P. sinensis. As UT-A2 is known to be a facilitative urea transporter, it is logical to deduce that it was localized in the basolateral membrane of the buccopharyngeal epithelium, and that another type of primary or secondary active urea transporter yet to be identified was present in the apical membrane. The ability to excrete urea through the mouth instead of the kidney might have facilitated the ability of P. sinensis and other soft-shelled turtles to successfully invade the brackish and/or marine environment.

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Sodium-dependent net urea transport in rat initial inner medullary collecting ducts.

Cited by 57 publications

References 25 publications

Active sodium-urea counter-transport is inducible in the basolateral membrane of rat renal initial inner medullary collecting ducts.

Active sodium-urea counter-transport is inducible in the basolateral membrane of rat renal initial inner medullary collecting ducts.

Maturational Changes in Rabbit Renal Brush Border Membrane Vesicle Urea Permeability • 1830

The Chinese soft-shelled turtle,Pelodiscus sinensis, excretes urea mainly through the mouth instead of the kidney

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