Figure 7. pH_i dependence of apical and basolateral Na⁺-H⁺ antiporters.

Both types of vesicles were equilibrated for 120 min at ambient temperature in a medium consisting of 300 mM mannitol, 40 mM TMA-nitrate, 3 mM EGTA, and with either 100 mM Tris-Mes at pH 5.50, 5.80, 6.10, 6.50, or with 100 mM Tris-Hepes at pH 7.00 and 7.50. The membrane vesicles were then diluted 1 : 9 and incubated for 9 s at 25 °C in 0.1 mM ²²Na⁺, 300 mM mannitol, 40 mM TMA-nitrate, 3 mM EGTA, and 100 mM Tris-Hepes, pH 7.5. Data were normalized as a percentage of the maximal rate of ²²Na⁺ uptake at pH 5.50. Levels of background influx that were not inhibitable by 0.5 mM DMA were subtracted from the total influx. Values represent the mean of nine experiments on three separate BLMV (×) and LMV (○) preparations.