Figure 2. Intracellular CO₂-dependent buffering.

A, intracellular buffering doubles on switching from Hepes to CO₂/HCO₃⁻-buffered conditions. The trace shows a ratiometric recording of pH_i. Superfusates were Cl⁻ free (gluconate substituted). An acetate prepulse (20 mM) was performed initially in Hepes, then (40 mM) in CO₂/HCO₃⁻-buffered solutions (same pH_o= 7.40). B, total intracellular buffering power (β_tot) in CO₂/HCO₃⁻-buffered conditions. Experimental protocol: a 40 mM acetate prepulse was executed in Cl⁻-free, 5 % CO₂/HCO₃⁻-buffered solution (pH_o 7.40) and the subsequent steady-state rise of pH_i used to calculate intracellular buffering power (β_tot). This has been plotted versus pH_i at the mid-point of the rise of intracellular HCO₃⁻ following acetate removal (see text for details). Data have been pooled from several cells and averaged for the following 0.1 pH_i ranges (•) starting at pH 6.90, with sample sizes, n = 8, 9, 6, 19 and 20. Also plotted (lower continuous line) is the relationship between intrinsic buffering capacity (β_i) and pH_i over the same pH_i range (6.90-7.38) calculated from eqn (1) in Results. C,β_CO2 in the cardiac cell. At a given pH_i, the difference between the mean experimental values of β_tot (• in B) and the value of β_i determined from eqn (1) (continuous curve in B) gives β_CO2. This difference has been plotted versus pH_i in C (○). The continuous line drawn through the data is the theoretical value of β_CO2vs. pH_i for a cell open to CO₂, and has been calculated from eqn (2) in Results.