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Effects of Intracellular and Extracellular Carbonic Anhydrase on the Influx of CO2 in a Xenopus Oocyte: Insights with a Mathematical Model
Author(s) -
Occhipinti Rossana,
MusaAziz Raif,
Calvetti Daniela,
Somersalo Erkki,
Boron Walter F
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.1039.25
Subject(s) - intracellular , extracellular , xenopus , chemistry , oocyte , intracellular ph , carbonic anhydrase , tortuosity , biophysics , transporter , biochemistry , microbiology and biotechnology , biology , enzyme , gene , embryo , organic chemistry , porosity
Carbonic anhydrases (CAs) catalyze the interconversion of CO 2 and HCO 3 , playing a key role in acid‐base metabolism. Musa‐Aziz et al (ASN‐2005) showed that exposing oocytes to 1.5% CO 2 /10 mM HCO 3 (pH o =7.5) causes intracellular pH (pH i ) to fall and surface pH (pH S ) to rise transiently and then decay, reflecting CO 2 influx. Injecting CA II into oocytes accelerates the pH i decline and amplifies the pH S spike. Expressing CAIV on the extracellular surface causes an even faster pH i decline and higher pH S spike. Musa‐Aziz et al propose that both CAII and CAIV enhance CO 2 influx by maximizing transmembrane CO 2 gradients. We explored the above results with a three‐dimensional mathematical model of a Xenopus oocyte, where simultaneous diffusion and reaction processes (competing equilibria among HCO 3 and non‐HCO 3 buffers) are modeled in both the extracellular unconvected solution (EUS) and intracellular fluid. We show how catalysis by CA and tortuosity factors, vitelline membrane, and solute mobilities influence the pH i and pH s profiles. The model predicts i) faster pH i decay when CAII activity is implemented and, in the presence of CAIV, ii) faster pH i decay when solute mobility in the EUS is reduced (mimicking the presence of the vitelline membrane and of the pH s electrode). Implementation of intracellular tortuosity factor explains the observed delay in the initial pH i decay.