Genomics of Urea Transport and Catabolism in Cyanobacteria: Biotechnological Implications

Our previous studies have detailed a novel facilitative UT-B urea transporter isoform, bUT-B2. Despite the existence of mouse and human orthologs, the functional characteristics of UT-B2 remain undefined. In this report, we produced a stable MDCK cell line that expressed bUT-B2 protein and investigated the transepithelial urea flux across cultured cell monolayers. We observed a large basal urea flux that was significantly reduced by known inhibitors of facilitative urea transporters; 1,3 dimethylurea ( P < 0.001, n = 17), thionicotinamide ( P < 0.05, n = 11), and phloretin ( P < 0.05, n = 9). Pre-exposure for 1 h to the antidiuretic hormone vasopressin had no effect on bUT-B2-mediated urea transport (NS, n = 3). Acute vasopressin exposure for up to 30 min also failed to elicit any transient response (NS, n = 9). Further investigation confirmed that bUT-B2 function was not affected by alteration of intracellular cAMP (NS, n = 4), intracellular calcium (NS, n = 3), or protein kinase activity (NS, n = 4). Finally, immunoblot data suggested a possible role for glycosylation in regulating bUT-B2 function. In conclusion, this study showed that bUT-B2-mediated transepithelial urea transport was constitutively activated and unaffected by known regulators of renal UT-A urea transporters.

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Dynamics of urea transport between blood and cerebrospinal fluid

Journal of Biomechanics ◽

10.1016/0021-9290(71)90002-9 ◽

1971 ◽

Vol 4 (3) ◽

pp. 175-184 ◽

Cited By ~ 1

Author(s):

William T. Gormley ◽

Philip R. Yarnell ◽

Richard L. Bell

Keyword(s):

Cerebrospinal Fluid ◽

Urea Transport

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The mechanisms of urea transport by early life stages of rainbow trout (Oncorhynchus mykiss)

Journal of Experimental Biology ◽

10.1242/jeb.203.20.3199 ◽

2000 ◽

Vol 203 (20) ◽

pp. 3199-3207 ◽

Cited By ~ 5

Author(s):

C.M. Pilley ◽

P.A. Wright

Keyword(s):

Rainbow Trout ◽

Oncorhynchus Mykiss ◽

Urea Transport ◽

Early Life Stages ◽

Urea Transporter ◽

Urea Excretion ◽

Rainbow Trout Oncorhynchus Mykiss ◽

Collecting Ducts ◽

External Water ◽

Very High

We tested the hypothesis that urea transport in rainbow trout (Oncorhynchus mykiss) embryos is dependent, in part, on a bidirectional urea-transport protein. Acute exposure to phloretin and urea analogs [acetamide, thiourea, 1,(4-nitrophenyl)-2-thiourea] reversibly inhibited urea excretion from the embryos to the external water. Unidirectional urea influx was inhibited by acetamide and thiourea, with IC(50) values of 0.04 and 0.05 mmol l(−1), respectively. Influx of urea from the external water to the embryo tended to saturate at elevated external urea concentrations (V(max)=10.50 nmol g(−1) h(−1); K(m)=2 mmol l(−1)). At very high urea concentrations (20 mmol l(−1)), however, a second, non-saturable component was apparent. These results indicate that urea excretion in trout embryos is dependent, in part, on a phloretin-sensitive facilitated urea transporter similar to that reported in mammalian inner medullary collecting ducts and elasmobranch kidney.

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Urea transport B gene induces melanoma B16 cell death via activation of p53 and mitochondrial apoptosis

Cancer Science ◽

10.1111/cas.13825 ◽

2018 ◽

Vol 109 (12) ◽

pp. 3762-3773 ◽

Cited By ~ 1

Author(s):

Lianqin Liu ◽

Yuxin Sun ◽

Yunxia Zhao ◽

Qian Wang ◽

Hua Guo ◽

...

Keyword(s):

Cell Death ◽

Mitochondrial Apoptosis ◽

Urea Transport ◽

Melanoma B16

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Osmotic stability of red cells in renal circulation requires rapid urea transport

AJP Cell Physiology ◽

10.1152/ajpcell.1988.254.5.c669 ◽

1988 ◽

Vol 254 (5) ◽

pp. C669-C674 ◽

Cited By ~ 70

Author(s):

R. I. Macey ◽

L. W. Yousef

Keyword(s):

Lipid Bilayers ◽

Physiological Role ◽

Renal Medulla ◽

Red Cells ◽

Facilitated Diffusion ◽

Urea Transport ◽

Permeability Characteristics ◽

Cortex Cell ◽

Cell Stability ◽

Michaelis Constants

Urea transport by the human erythrocyte occurs via an asymmetric-facilitated diffusion system with high Michaelis constants and high maximal velocities; the equivalent permeability in the limit of zero urea concentration is approximately 10(-3) cm/s (J. Gen. Physiol. 81: 221-237, 239-253, 1983). A physiological role for this system is revealed by numerical integration of the appropriate equations that show that rapid urea transport is essential for red cell stability in passing through the renal medulla. The calculation compares two cells. Cell A transports urea with permeability characteristics of normal red cells; cell B has urea permeability similar to lipid bilayers. On entering the hypertonic medulla, both cells shrink, but only B swells on leaving the medulla. The osmotic stress for cell B is greater than for A. Cell B is close to hypertonic hemolysis in the medulla and to hypotonic hemolysis in the cortex. Cell B remains swollen for some time after its exit; the resulting decreased deformability presents a hazard if B reenters the microcirculation. Furthermore, cell B removes a significant fraction of the filtered load of urea and compromises the osmotic gradients in the medulla.

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Carrier-mediated urea transport across the mitochondrial membrane of an elasmobranch (Raja erinacea) and a teleost (Oncorhynchus mykiss) fish

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00251.2007 ◽

2008 ◽

Vol 294 (6) ◽

pp. R1947-R1957 ◽

Cited By ~ 2

Author(s):

T. M. Rodela ◽

J. S. Ballantyne ◽

P. A. Wright

Keyword(s):

Oncorhynchus Mykiss ◽

Mitochondrial Membrane ◽

Liver Mitochondria ◽

Reverse Direction ◽

Maximal Velocity ◽

Urea Transport ◽

Submitochondrial Particles ◽

Raja Erinacea ◽

Urea Uptake ◽

High Concentrations

In osmoregulating teleost fish, urea is a minor nitrogen excretory product, whereas in osmoconforming marine elasmobranchs it serves as the major tissue organic solute and is retained at relatively high concentrations (∼400 mmol/l). We tested the hypothesis that urea transport across liver mitochondria is carrier mediated in both teleost and elasmobranch fishes. Intact liver mitochondria in rainbow trout ( Oncorhynchus mykiss) demonstrated two components of urea uptake, a linear component at high concentrations and a phloretin-sensitive saturable component [Michaelis constant ( Km) = 0.58 mmol/l; maximal velocity ( Vmax) = 0.12 μmol·h−1·mg protein−1] at lower urea concentrations (<5 mmol/l). Similarly, analysis of urea uptake in mitochondria from the little skate ( Raja erinacea) revealed a phloretin-sensitive saturable transport ( Km= 0.34 mmol/l; Vmax= 0.054 μmol·h−1·mg protein−1) at low urea concentrations (<5 mmol/l). Surprisingly, urea transport in skate, but not trout, was sensitive to a variety of classic ionophores and respiration inhibitors, suggesting cation sensitivity. Hence, urea transport was measured in the reverse direction using submitochondrial particles in skate. Transport kinetics, inhibitor response, and pH sensitivity were very similar in skate submitochondrial particle submitochondrial particles ( Km= 0.65 mmol/l, Vmax= 0.058 μmol·h−1·mg protein−1) relative to intact mitochondria. We conclude that urea influx and efflux in skate mitochondria is dependent, in part, on a bidirectional proton-sensitive mechanism similar to bacterial urea transporters and reminiscent of their ancestral origins. Rapid equilibration of urea across the mitochondrial membrane may be vital for cell osmoregulation (elasmobranch) or nitrogen waste excretion (teleost).

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Ultramicrodetermination of vasopressin-regulated urea transporter protein in microdissected renal tubules

AJP Renal Physiology ◽

10.1152/ajprenal.1997.272.4.f531 ◽

1997 ◽

Vol 272 (4) ◽

pp. F531-F537 ◽

Cited By ~ 9

Author(s):

B. K. Kishore ◽

J. Terris ◽

P. Fernandez-Llama ◽

M. A. Knepper

Keyword(s):

Collecting Duct ◽

Enzyme Linked Immunosorbent Assay ◽

Apical Plasma Membrane ◽

Renal Tubules ◽

Urea Transport ◽

Urea Transporter ◽

Transporter Protein ◽

Low Protein ◽

Collecting Duct Cells ◽

Medullary Collecting Duct

The vasopressin-regulated urea transporter (VRUT) is a 97-kDa protein (also called “UT-1”) responsible for facilitated urea transport across the apical plasma membrane of inner medullary collecting duct (IMCD) cells. To determine the abundance of VRUT protein in collecting duct cells of the rat, we designed a sensitive fluorescence-based enzyme-linked immunosorbent assay capable of detecting <5 fmol of VRUT protein. In collecting duct segments, measurable VRUT was found in microdissected IMCD segments but not in other portions of the collecting duct. In the mid-IMCD, the measured level averaged 5.3 fmol/mm tubule length, corresponding to approximately 5 million copies of VRUT per cell. Thus VRUT is extremely abundant in the IMCD, accounting, in part, for the extremely high urea permeability of this segment. Feeding a low-protein diet (8% protein) markedly decreased urea clearance but did not alter the quantity of VRUT protein in the IMCD. Thus increased urea transport across the collecting duct with dietary protein restriction is not a consequence of increased expression of VRUT. Based on urea fluxes measured in the IMCD and our measurements of the number of copies of VRUT, we estimate a turnover number of > or = 0.3-1 x 10(5) s. In view of the large magnitude of this value and previously reported biophysical properties of urea transport in collecting ducts, we hypothesize that the VRUT may function as a channel rather than a carrier.

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Urea transport

Fish Physiology - Nitrogen Excretion ◽

10.1016/s1546-5098(01)20009-0 ◽

2001 ◽

pp. 279-307 ◽

Cited By ~ 14

Author(s):

P.J. Walsh ◽

C.P. Smith

Keyword(s):

Urea Transport

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