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Weinstein2000_OMCD

ABSTRACT: This a model from the article: A mathematical model of the outer medullary collecting duct of the rat. Weinstein AM. Am J Physiol Renal Physiol 2000 Jul;279(1):F24-45 10894785 , Abstract: A mathematical model of the outer medullary collecting duct (OMCD) has been developed, consisting of alpha-intercalated cells and a paracellular pathway, and which includes Na(+), K(+), Cl(-), HCO(3)(-), CO(2), H(2)CO(3), phosphate, ammonia, and urea. Proton secretion across the luminal cell membrane is mediated by both H(+)-ATPase and H-K-ATPase, with fluxes through the H-K-ATPase given by a previously developed kinetic model (Weinstein AM. Am J Physiol Renal Physiol 274: F856-F867, 1998). The flux across each ATPase is substantial, and variation in abundance of either pump can be used to control OMCD proton secretion. In comparison with the H(+)-ATPase, flux through the H-K-ATPase is relatively insensitive to changes in lumen pH, so as luminal acidification proceeds, proton secretion shifts toward this pathway. Peritubular HCO(3)(-) exit is via a conductive pathway and via the Cl(-)/HCO(3)(-) exchanger, AE1. To represent AE1, a kinetic model has been developed based on transport studies obtained at 38 degrees C in red blood cells. (Gasbjerg PK, Knauf PA, and Brahm J. J Gen Physiol 108: 565-575, 1996; Knauf PA, Gasbjerg PK, and Brahm J. J Gen Physiol 108: 577-589, 1996). Model calculations indicate that if all of the chloride entry via AE1 recycles across a peritubular chloride channel and if this channel is anything other than highly selective for chloride, then it should conduct a substantial fraction of the bicarbonate exit. Since both luminal membrane proton pumps are sensitive to small changes in cytosolic pH, variation in density of either AE1 or peritubular anion conductance can modulate OMCD proton secretory rate. With respect to the OMCD in situ, available buffer is predicted to be abundant, including delivered HCO(3)(-) and HPO(4)(2-), as well as peritubular NH(3). Thus, buffer availability is unlikely to exert a regulatory role in total proton secretion by this tubule segment. This model was taken from the CellML repository and automatically converted to SBML. The original model was: Weinstein AM. (2000) - version=1.0 The original CellML model was created by: Jonna Terkildsen j.terkildsen@auckland.ac.nz The University of Auckland This model originates from BioModels Database: A Database of Annotated Published Models (http://www.ebi.ac.uk/biomodels/). It is copyright (c) 2005-2011 The BioModels.net Team. To the extent possible under law, all copyright and related or neighbouring rights to this encoded model have been dedicated to the public domain worldwide. Please refer to CC0 Public Domain Dedication for more information. In summary, you are entitled to use this encoded model in absolutely any manner you deem suitable, verbatim, or with modification, alone or embedded it in a larger context, redistribute it, commercially or not, in a restricted way or not.. To cite BioModels Database, please use: Li C, Donizelli M, Rodriguez N, Dharuri H, Endler L, Chelliah V, Li L, He E, Henry A, Stefan MI, Snoep JL, Hucka M, Le Novère N, Laibe C (2010) BioModels Database: An enhanced, curated and annotated resource for published quantitative kinetic models. BMC Syst Biol., 4:92.

SUBMITTER: Camille Laibe

PROVIDER: MODEL1006230037 | BioModels | 2005-01-01

REPOSITORIES: BioModels

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A mathematical model of the outer medullary collecting duct of the rat.

Weinstein A M AM

American journal of physiology. Renal physiology 20000701 1

A mathematical model of the outer medullary collecting duct (OMCD) has been developed, consisting of alpha-intercalated cells and a paracellular pathway, and which includes Na(+), K(+), Cl(-), HCO(3)(-), CO(2), H(2)CO(3), phosphate, ammonia, and urea. Proton secretion across the luminal cell membrane is mediated by both H(+)-ATPase and H-K-ATPase, with fluxes through the H-K-ATPase given by a previously developed kinetic model (Weinstein AM. Am J Physiol Renal Physiol 274: F856-F867, 1998). The ...[more]

PMID: 10894785

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Project description:A mathematical model of the pancreatic duct cell generating high bicarbonate concentrations in pancreatic juice David C Whitcomb, G Bard Ermentrout, Pancreas 2004 29:e30-40; PubMedID:15257112 Abstract: OBJECTIVE: To develop a simple, physiologically based mathematical model of pancreatic duct cell secretion using experimentally derived parameters that generates pancreatic fluid bicarbonate concentrations of >140 mM after CFTR activation. METHODS: A new mathematical model was developed simulating a duct cell within a proximal pancreatic duct and included a sodium-2-bicarbonate cotransporter (NBC) and sodium-potassium pump (NaK pump) on a chloride-impermeable basolateral membrane, CFTR on the luminal membrane with 0.2 to 1 bicarbonate to chloride permeability ratio. Chloride-bicarbonate antiporters (Cl/HCO3 AP) were added or subtracted from the basolateral (APb) and luminal (APl) membranes. The model was integrated over time using XPPAUT. RESULTS: This model predicts robust, NaK pump-dependent bicarbonate secretion with opening of the CFTR, generates and maintains pancreatic fluid secretion with bicarbonate concentrations >140 mM, and returns to basal levels with CFTR closure. Limiting CFTR permeability to bicarbonate, as seen in some CFTR mutations, markedly inhibited pancreatic bicarbonate and fluid secretion. CONCLUSIONS: A simple CFTR-dependent duct cell model can explain active, high-volume, high-concentration bicarbonate secretion in pancreatic juice that reproduces the experimental findings. This model may also provide insight into why CFTR mutations that predominantly affect bicarbonate permeability predispose to pancreatic dysfunction in humans. This SBML version of the model was created directly from the XPPAUT code found in the appendix with the exception of the parameter vr, the ratio between the duct cell volume and the duct lumen, which is defined inversely to the main text in the XPPAUT code. vr was defined as the ratio of the duct cell volume to the duct lumen volume as in the main text. The model reproduces the figures found in the article. The model uses initial assignments for the lumen volume and events to trigger CFTR opening, so only tools supporting these features can be used to simulate it (eg. Copasi and SBW/Roadrunner).

Project description:Analysis of epithelial explants injected with the intracellular domain of Notch (ICD) to block the formation of multi-ciliate and proton secreting cells or with dominant negative human Mastermind (HMM) to induce the formation of ectopic multi-ciliate and proton secreting cells. Results show which genes are up or down-regulated when HMM is compared to ICD. Specialized epithelial cells in the amphibian skin play important roles in ion transport, but how they arise developmentally is largely unknown. Here we show that proton-secreting cells (PSCs) differentiate in the X. laevis larval skin soon after gastrulation, based on the expression of “kidney” specific form of the H+v-ATPase that localizes to the plasma membrane, orthologs of the Cl-/HCO3- antiporters ae1 and pendrin, and two isoforms of carbonic anhydrase. Like PSCs in other species, we show that the expression of these genes is likely to be driven by an ortholog of foxi1, which is also sufficient to promote the formation of PSC precursors. Strikingly, the PSCs form in the skin as two distinct subtypes that resemble the alpha- and beta-intercalated cells of the kidney. The alpha-subtype expresses ae1 and localizes H+v-ATPases to the apical plasma membrane, whereas the beta-subtype expresses pendrin and localizes the H+v-ATPase cytosolically or basolaterally. These two subtypes are specified during early differentiation, and can be distinguished based on the expression of ubp1, a transcription factor in the grainyhead family. Finally, we show that ectopic expression ubp1 is sufficient to promote the differentiation of beta-subtypes while repressing alpha-subtypes. These results have implications for how PSCs are specified in vertebrates and become functionally heterogeneous. 2-cell stage Xenopus embryos were injected with synthetic mRNA encoding ICD or HMM. At stage 9/10 the presumptive ectoderm was cut off the embryo and cultured on a fibronectin coated coverslip. At stage 22 RNA was harvested from explants and used as the starting material for arrays.

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Weinstein2000_OMCD

Publications

A mathematical model of the outer medullary collecting duct of the rat.

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