Maturational Changes in Rabbit Renal Basolateral Membrane Vesicle Osmotic Water Permeability

Quigley, Raymond; Gupta, Neena; Lisec, Amber; Baum, Michel

doi:10.1007/s002320001031

Cited by 19 publications

(23 citation statements)

References 23 publications

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“…During renal development, there is a maturational increase in proximal tubule AQP1 expression (6,21,22). However, we found that the osmotic water permeability (P f ) in the neonatal rabbit proximal tubule was actually equal to or greater than that of the adult proximal tubule (20).…”

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confidence: 63%

“…The importance of AQP1 to water transport by this nephron segment is evidenced by the fact that mice lacking AQP1 have a much lower rate of fluid transport than wild-type mice (25). Previous studies in the adult kidney have also indicated that most of the water transport through the proximal tubule is transcellular, not paracellular, and that the intracellular compartment may be responsible for more than onehalf of the resistance to water flow (4, 16).During renal development, there is a maturational increase in proximal tubule AQP1 expression (6,21,22). However, we found that the osmotic water permeability (P f ) in the neonatal rabbit proximal tubule was actually equal to or greater than that of the adult proximal tubule (20).…”

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confidence: 99%

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Water transport in neonatal and adult rabbit proximal tubules

Quigley¹,

Baum

2002

American Journal of Physiology-Renal Physiology

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Quigley, Raymond, and Michel Baum. Water transport in neonatal and adult rabbit proximal tubules. Am J Physiol Renal Physiol 283: F280-F285, 2002; 10.1152/ajprenal.00341.2001.-We have recently demonstrated that although the osmotic water permeability (P f) of neonatal proximal tubules is higher than that of adult tubules, the P f of brush-border and basolateral membrane vesicles from neonatal rabbits is lower than that of adults. The present study examined developmental changes in the water transport characteristics of proximal convoluted tubules (PCTs) in neonatal (9-16 days old) and adult rabbits to determine whether the intracellular compartment or paracellular pathway is responsible for the maturational difference in transepithelial water transport. The permeability of n-butanol was higher in the neonatal PCT than the adult PCT at all temperatures examined, whereas the diffusional water permeability was identical. Increasing the osmotic gradient increased volume absorption in both the neonatal and the adult PCT to the same degree. The P f was not different between the neonatal and the adult PCT at any osmotic gradient studied. To assess solvent drag as a measure of the paracellular transport of water, the effect of the osmotic gradient on mannitol and chloride transport were measured. There was no change in chloride or mannitol transport with the increased osmotic gradient in either group, indicating that there was no detectable paracellular water movement. In addition, the mannitol permeability of the neonatal PCT was found to be lower than that of the adult PCT with the isotonic bath (8.97 Ϯ 4.01 vs. 40.49 Ϯ 13.89 m/s, P Ͻ 0.05). Thus the intracellular compartment of the neonatal PCT has a lower resistance for water transport than the adult PCT and is responsible for the higher than expected P f in the neonatal PCT.proximal convoluted tubules; development; butanol permeability; diffusional water permeability; in vitro microperfusion WATER TRANSPORT ACROSS CELLULAR membranes is a fundamental biological process that occurs either by diffusion through the lipid bilayer or by movement through specific water channels (aquaporins) (3,11,28). There is also evidence that water can traverse across other membrane transport proteins (12). Transport of water through the lipid bilayer is characterized by a high activation energy (Ͼ9 kcal ⅐ mol Ϫ1 ⅐ degree Ϫ1 ) and resistance to inhibition by mercury, whereas water movement through aquaporins is characterized by a low activation energy (ϳ4-5 kcal ⅐ mol Ϫ1 ⅐ degree Ϫ1) and is inhibited by mercury for most aquaporin isoforms (28).The proximal tubule of the mammalian kidney is responsible for reabsorbing the bulk of the glomerular ultrafiltrate (24). This process is nearly isosmotic because the proximal tubule has a very high water permeability, which is thought to be due to the constitutive presence of the water channel aquaporin-1 (AQP1). The importance of AQP1 to water transport by this nephron segment is evidenced by the fact that mice lacking AQP1 have a much lower r...

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confidence: 63%

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confidence: 99%

Water transport in neonatal and adult rabbit proximal tubules

Quigley¹,

Baum

2002

American Journal of Physiology-Renal Physiology

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“…In hypothyroid animals, the levels of the active compound T 3 were reduced by approximately one-third compared with control, euthyroid animals. T 3 -replacement was confirmed to be effective by the high levels of T 3 measured 2 h after the last dose of T 3 .…”

Section: Serum Thyroid Levelsmentioning

confidence: 81%

“…Five raw tracings were averaged and analyzed subsequently. P f was calculated as previously described (3). Briefly, the osmotic water permeability was calculated from the stop-flow light scattering data as described by Van Heeswijk et al (10).…”

Section: Animalsmentioning

confidence: 99%

“…This occurs in a nearly isoosmotic manner due to the high water permeability of this segment. We have previously demonstrated that the osmotic water permeability of both apical (brush border) and basolateral membranes increased during postnatal development (2,3). In both membranes, this was accompanied by an increase in aquaporin-1 (AQP1) expression; the predominant water channel in proximal tubular membranes (4).…”

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Hypothyroidism Increases Osmotic Water Permeability (Pf) in the Developing Renal Brush Border Membrane

et al. 2003

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The osmotic water permeability (P f ) of the rabbit proximal tubule brush border membrane vesicles (BBMV) increases during maturation and is mediated by an increase in aquaporin-1 (AQP1) protein expression. Serum thyroid hormone levels increase after birth and have been shown to play a role in the maturation of other renal transport functions. We examined the hypothesis that thyroid hormone plays a role in the maturational increase in osmotic water permeability. Hypothyroidism was induced by addition of 0.1% propylthiouracil (PTU) to the drinking water of pregnant rabbits (starting 9 d before delivery) and was continued until the rabbits were studied as adults (9-11 wk). Some animals received thyroid hormone replacement by daily injection with triiodothyronine (T 3 ; 10 g/100 g body weight) for three days before study. P f was found to be higher in BBMV from hypothyroid (82.7 Ϯ 5.5 m/s) than from euthyroid (60.6 Ϯ 4.0 m/s) and T 3 -replacement rabbits (69.0 Ϯ 5.0 m/s) (p Ͻ 0.05). The activation energy (E a ; in kcal/deg⅐mol) of P f was not different among the three experimental groups (euthyroid 5.6 Ϯ 0.9, hypothyroid 4.9 Ϯ 0.8, T 3 -replacement 5.0 Ϯ 1.0; p ϭ NS), nor was the percentage mercury inhibition of P f (euthyroid 66.5 Ϯ 5.3, hypothyroid 74.2 Ϯ 3.2 and T 3 -replacement 73.1 Ϯ 4.3; p ϭ NS). AQP1 expression, measured by immunoblotting, was highest in BBMV from hypothyroid rabbits (p Ͻ 0.05). Membrane fluidity, measured as steady-state generalized polarization (GP) of Laurdan, which is inversely related to membrane fluidity, was significantly different between the three groups (GP: euthyroid 0.307 Ϯ 0.004, hypothyroid 0.271 Ϯ 0.004 and T 3 -replacement 0.287 Ϯ 0.003; for all p Ͻ 0.05). These data demonstrate that the maturational increase in thyroid hormone levels is not responsible for the maturational increase in water transport. Surprisingly, congenital hypothyroidism in rabbits is associated with an increased P f when rabbits are studied as adults. The higher P f in hypothyroid adult rabbits is due to a higher expression of AQP1 protein as well as a greater membrane fluidity than in euthyroid rabbits. The proximal tubule reabsorbs approximately two-thirds of the glomerular ultrafiltrate (1). This occurs in a nearly isoosmotic manner due to the high water permeability of this segment. We have previously demonstrated that the osmotic water permeability of both apical (brush border) and basolateral membranes increased during postnatal development (2, 3). In both membranes, this was accompanied by an increase in aquaporin-1 (AQP1) expression; the predominant water channel in proximal tubular membranes (4).The factors that are responsible for the maturational change in proximal tubule water transport and AQP 1 expression remain unknown. Thyroid hormone levels rise postnatally (5, 6) and have been shown to be a factor in developmental changes in proximal tubular function, including NaCl transport (7), Na ϩ /H ϩ -antiporter activity (5) and phosphate transport (6). The role of thyroid hormone with regard to ...

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Urea Transport in the Kidney

Klein

Blount

Sands

2011

Comprehensive Physiology

124

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Urea transport proteins were initially proposed to exist in the kidney in the late 1980s when studies of urea permeability revealed values in excess of those predicted by simple lipid-phase diffusion and paracellular transport. Less than a decade later, the first urea transporter was cloned. Currently, the SLC14A family of urea transporters contains two major subgroups: SLC14A1, the UT-B urea transporter originally isolated from erythrocytes; and SLC14A2, the UT-A group with six distinct isoforms described to date. In the kidney, UT-A1 and UT-A3 are found in the inner medullary collecting duct; UT-A2 is located in the thin descending limb, and UT-B is located primarily in the descending vasa recta; all are glycoproteins. These transporters are crucial to the kidney's ability to concentrate urine. UT-A1 and UT-A3 are acutely regulated by vasopressin. UT-A1 has also been shown to be regulated by hypertonicity, angiotensin II, and oxytocin. Acute regulation of these transporters is through phosphorylation. Both UT-A1 and UT-A3 rapidly accumulate in the plasma membrane in response to stimulation by vasopressin or hypertonicity. Long-term regulation involves altering protein abundance in response to changes in hydration status, low protein diets, adrenal steroids, sustained diuresis, or antidiuresis. Urea transporters have been studied using animal models of disease including diabetes mellitus, lithium intoxication, hypertension, and nephrotoxic drug responses. Exciting new animal models are being developed to study these transporters and search for active urea transporters. Here we introduce urea and describe the current knowledge of the urea transporter proteins, their regulation, and their role in the kidney.

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Maturational Changes in Rabbit Renal Basolateral Membrane Vesicle Osmotic Water Permeability

Cited by 19 publications

References 23 publications

Water transport in neonatal and adult rabbit proximal tubules

Water transport in neonatal and adult rabbit proximal tubules

Hypothyroidism Increases Osmotic Water Permeability (Pf) in the Developing Renal Brush Border Membrane

Urea Transport in the Kidney

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