Fig. 12.

Simulations of pH_i and pH_S transients for the addition of extracellular 10% CO₂/66 mM HCO₃⁻, with graded increases in levels of extracellular HEPES. A: “control” oocyte. B: “CA IV” oocyte. This figure differs from Fig. 11 in that, here, the CO₂/HCO₃⁻ levels are ∼6.6-fold higher. The pH_i transients, calculated at a depth of ∼50 μm, are represented by the red lower trajectories, and pH_S, by the green upper trajectories. At the indicated time, we switched the extracellular solution from CO₂/HCO₃⁻-free “ND96” to 1) CO₂/HCO₃⁻ + 1 mM HEPES, or 2) CO₂/HCO₃⁻ + 5 mM HEPES, or 3) CO₂/HCO₃⁻ + 25 mM HEPES. The dashed black lines through the initial portions of the pH_i transients for CO₂ application represent the maximal rates of pH_i change (negative direction) predicted by the model. The upward arrows near the pH_S records represent maximal changes in pH_S (positive direction).