Fig. 1.

Main features of the revised mathematical model. Following the approach of Somersalo et al. (22), we assume that the oocyte is a perfectly symmetric sphere of radius R, surrounded by a thin layer of extracellular unconvected fluid (EUF) of thickness d. The EUF is in turn surrounded by the bulk extracellular fluid (BECF), which is an infinite reservoir for all solutes. Within the BECF, convection could occur (though it is not included in the present model), but no reaction or diffusion. Solutes can diffuse between the BECF and EUF. In both the intracellular fluid (ICF) and EUF, reaction and diffusion occur, but no convection. The buffer reactions occurring in the ICF and EUF (illustrated in the inset in the bottom left corner) are: the CO₂/HCO₃⁻ buffer reactions (including the slow conversion of CO₂ into H₂CO₃ and vice versa) and a single non-CO₂/HCO₃⁻ buffer (HA/A⁻). New features of the model include (starting from the inside of the cell and moving outward): 1) reduced water content of cytosol, 2) reduced cytosolic diffusion constants, 3) refined CA II activity, 4) layer of intracellular vesicles (magnification in top left corner), 5) reduced membrane CO₂ permeability, 6) microvilli (magnification in top right corner), 7) refined CA IV activity, 8) vitelline membrane (magnification on lower edge), and 9) a new simulation protocol for the delivery and removal of the bulk extracellular CO₂/HCO₃⁻ solution. The inset in the bottom right corner explains the spatial discretization for the numerical solution near the plasma membrane (PM). EM, extracellular surface of the PM; IM, intracellular surface of the PM.