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A Reaction‐Diffusion Model of Acid‐Base Balance in a Xenopus Oocyte
Author(s) -
Somersalo Erkki,
Occhipinti Rossana,
Boron Walter F,
Calvetti Daniela
Publication year - 2011
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.25.1_supplement.1129.4
Subject(s) - xenopus , oocyte , acid–base homeostasis , balance (ability) , chemistry , diffusion , base (topology) , microbiology and biotechnology , biology , mathematics , biochemistry , physics , neuroscience , thermodynamics , mathematical analysis , gene , embryo
We present a new three‐dimensional mathematical model of a Xenopus oocyte. The model assumes that the oocyte is a perfectly symmetric spherical cell surrounded by the extracellular unconvected solution (EUS) which in turn is surrounded by the stirred bulk extracellular solution (BECS). The oocyte plasma membrane is assumed to be infinitely thin and permeable only to CO 2 . Using Fick's second law of diffusion and the law of mass action, diffusion and reaction processes are modeled in both EUS and intracellular fluid (ICF). The model accounts for the slow equilibration CO 2 + H 2 O ⇄ H 2 CO 3 as governed by the forward and reverse rate constants and for competing equilibria among the HCO 3 − and an indefinite number of non‐HCO 3 − buffers. We present the results of numerical simulations when, in addition to the CO 2 /HCO 3 − buffer, a single mobile non‐HCO 3 − buffer is present in the ICF and EUS. By solving the system of reaction‐diffusion equations we analyze how the profiles of pH and solutes change in time and space as a result of the CO 2 influx. Consistent with experimental data (Musa‐Aziz et al, PNAS, 2009; ASN 2005); the model predicts that applying extracellular 1.5% CO 2 /10 mM HCO 3 − (fixed pH of 7.50) causes the familiar fall in pH i and a rise followed by decay in pH S . We also show how the presence of two non‐HCO 3 − intracellular buffers with different mobilities and how the CO 2 membrane permeability affect the predictions of the model.