Fig. 2.

Intracellular pH (pH_i) and surface (pH_S) records during application and removal of 5 mM NH₃/NH₄⁺. a H₂O-injected oocyte. b AmtB EGFP-tagged expressing oocytes. At the indicated times, we switched the extracellular solution from ND96 to 5 mM NH₃/NH₄⁺ and then back again. b shows two representative experiments: on the left, pH_S at first decays rapidly and then more slowly, whereas on the right, pH_S decays slowly throughout the NH₃/NH₄⁺ exposure. In both a and b, the purple record is pH_S, the blue record is pH_i, and the brown record is V_m. The vertical gray bands represent periods during which the pH_S electrode was moved to the bulk ECF for calibration (fixed pH of 7.50). In H₂O oocytes, mean pH_i was 7.10 ± 0.04 before and 6.84 ± 0.06 during exposure to 5 mM NH₃/NH₄⁺ (n = 6; p = 0.005); the comparable mean V_m values were −43 ± 2 and − 25 ± 2 mV (n = 6; p = 0.0002). In AmtB oocytes, the mean pH_i was 7.14 ± 0.04 before and 6.98 ± 0.06 during exposure to 5 mM NH₃/NH₄⁺ (n = 8; p = 0.037); the comparable mean V_m values were −38 ± 4 and −26 ± 2 (n = 8; p = 0.010)