34 research outputs found

    Model results: flow of total ammonia (tAmm) in each structure under baseline conditions.

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    <p>Ammonia is reabsorbed in OM ascending limb of the loops of Henle (decreased flow), and partly recycled into descending limbs (increased flow) or secreted into the collecting ducts. The increase in ammonia flow in the OM descending limbs is also due to tubular ammonia production. Please note the different scale for total flow in the collecting ducts, whereas flows are given per tube in nephron segments and blood vessels.</p

    Parameter study.

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    <p>%changes in total ammonia flows resulting from multiplying each baseline parameter by 5: A) changes at the papillary tip of long loops, B) changes at the tip of short loops (outer-inner medullary junction), C) changes in total ammonia secretion into the collecting ducts, D) changes in urinary excretion. Parameters associated with ammonia recycling in the loops of Henle (especially of short nephrons, see B) are associated with the largest increase in urinary ammonia flow (D). The figure only shows the parameters that affect urinary ammonia excretion by at least 10%. Vmax<sup><i>AL</i></sup>: maximum rate of active transport of </p><p></p><p></p><p></p><p>NH<mn>4</mn><mo>+</mo></p><p></p><p></p><p></p> in thick ascending limbs; <p></p><p></p><p></p><p>P</p><p><mi>N</mi></p><p><mi>H</mi><mn>3</mn></p><p></p><p><mi>D</mi><mi>L</mi><mi>O</mi><mi>S</mi></p><p></p><p></p><p></p><p></p> / <p></p><p></p><p></p><p>P</p><p><mi>N</mi></p><p><mi>H</mi><mn>3</mn></p><p></p><p><mi>A</mi><mi>L</mi><mi>I</mi><mi>S</mi></p><p></p><p></p><p></p><p></p> / <p></p><p></p><p></p><p>P</p><p><mi>N</mi></p><p><mi>H</mi><mn>3</mn></p><p></p><p><mi>C</mi><mi>S</mi><mi>I</mi><mi>S</mi></p><p></p><p></p><p></p><p></p> NH<sub>3</sub> permeability of outer stripe descending limbs/ inner stripe ascending limbs/ inner stripe collecting ducts; <p></p><p></p><p></p><p>P</p><p><mi>N</mi></p><p><mi>H</mi><mn>4</mn><mo>+</mo></p><p></p><p><mi>D</mi><mi>V</mi><mi>R</mi><mi>I</mi><mi>S</mi></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p>NH<mn>4</mn><mo>+</mo></p><p></p><p></p><p></p> permeability in descending vasa recta of the inner stripe.<p></p

    Inhibition of NH<sub>3</sub> secretion in the DL OM (permeability PNH3DL OM=0) prevents ammonia recycling in the loops of Henle, which limits urinary ammonia excretion.

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    <p>The effect is more potent when ammonia reabsorption in the MTAL is increased (maximum rate of active transport </p><p></p><p></p><p></p><p>Vmax</p><p>NH<mn>4</mn><mo>+</mo></p>AL<p></p><mo>×</mo><mn>5</mn><p></p><p></p><p></p>).<p></p

    Rates of total ammonia production in the various tubular segments (pmol.min<sup>-1</sup>.mm<sup>-1</sup> tube) [15].

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    <p>Rates of total ammonia production in the various tubular segments (pmol.min<sup>-1</sup>.mm<sup>-1</sup> tube) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0134477#pone.0134477.ref015" target="_blank">15</a>].</p

    Impact of pH environment on urinary excretion of ammonia.

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    <p>The figure shows the percentage change in ammonia excretion rate and the urinary total ammonia concentration when the pH at the top of the interstitium is varied (thus changing the medullary pH profile).</p

    Model results (alternative baseline scenario): osmolality gradients (mOsm/KgH<sub>2</sub>O) obtained when the segments of the descending limbs are assumed to be water impermeable.

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    <p>Model results (alternative baseline scenario): osmolality gradients (mOsm/KgH<sub>2</sub>O) obtained when the segments of the descending limbs are assumed to be water impermeable.</p

    Model parameters.

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    <p>r: tube radius (<i>μ</i>m), Lp: hydraulic permeability, R: gas constant, T temperature (LpRT in 10<sup>-6</sup>mm.s<sup>-1</sup>.mosM<sup>-1</sup>), P permeability coefficient (10<sup>-5</sup>cm.s<sup>-1</sup>), <i>σ</i> reflexion coefficient, Vmax in nmole.mm<sup>-2</sup>.min<sup>-1</sup>, Km in mM, ΔV: transmembrane electrical potential in mV, Na: sodium, u: urea, NRS: non reabsorbable solute (see text for reference).</p><p>Model parameters.</p

    Model results: (A-B) NH4+ and NH<sub>3</sub> concentration profiles.

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    <p>In the outer medulla, passive diffusion gradients favor secretion of NH<sub>3</sub> into nephron segments and reabsorption of </p><p></p><p></p><p></p><p>NH<mn>4</mn><mo>+</mo></p><p></p><p></p><p></p>. (C-D) <p></p><p></p><p></p><p>NH<mn>4</mn><mo>+</mo></p><p></p><p></p><p></p> and NH<sub>3</sub> transmural fluxes profiles. Positive fluxes denote absorption, whereas negative fluxes represent secretion. Please note the different scales for total fluxes in the collecting ducts (nmol.min<sup>-1</sup>mm<sup>-1</sup>), whereas fluxes are given per tube in nephron segments and blood vessels (pmol.min<sup>-1</sup>mm<sup>-1</sup>.tube<sup>-1</sup>).<p></p

    Parameter analyses based on three alternative baseline scenarios.

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    <p>‘DL partly impermeable’: in this scenario, some sub-segments of the descending limbs are assumed to be water impermeable (the outer-stripe of superficial nephrons, the inner medullary segment of juxtamedullary nephrons whose loop of Henle bends within the first millimeter of the inner medulla, and the last 60% of inner medullary segment of juxtamedullary nephron which go deeper in the inner medulla). ‘no external osmoles’: in this scenario, the external osmoles concentrations in the inner medulla are set to 0. ‘No production’: ammonia production is set to 0. ‘Cortical Amm’: in this scenario, ammonia delivered to the collecting ducts is proportional to ammonia flow at the exit of the ascending limbs. The number of ‘+’ in ‘-’ corresponds to the percentage change of the rate of ammonia excretion from the corresponding baseline scenario: ‘-’ for -20% to -10%; ‘+’ for 10% to 20%; ‘++’ for 20% to 30%; ‘+++’ for 30% to 40%; ‘++++’ for > 40%.</p><p>Parameter analyses based on three alternative baseline scenarios.</p
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