FIGURE 5.

Intrinsic buffering capacity and pH_o were determined following blockade of Na-H exchange and V-ATPase acid extrusion by NMDG gluconate substitution of Na⁺ and Cl⁻. A, Na⁺ and Cl⁻ removal produced a 1.08 ± 0.08 pH units acidification in optic nerve astrocytes, and exposure to NH₄⁺ (20 mm) in the absence of acid extrusion mechanisms evoked an alkalinization. B, pH_o measured in optic nerve using ion-sensitive microelectrodes was increased by 0.08 pH units following Na⁺ and Cl⁻ removal. C and D, exposure to NH₄⁺ as in A (1–10 mm) resulted in increasing alkalinization. The buffering capacity (β_i) for each [NH₄⁺] concentration was calculated and plotted against the resulting pH_i. Note that the pH change has been extrapolated back to time 0 for each solution. All values are given as mean ± S.E.