Figure 5.

NCX_Mj is inhibited at low pH but does not transport H⁺. (A) Initial rates of Na⁺/⁴⁵Ca²⁺ antiport in the presence of a varying inwardly directed H⁺ gradient. Liposomes were preloaded with MES/Tris pH 6.3 buffer containing 100 mM NaCl and 100 µM EGTA and diluted into Na⁺-free reaction buffers with 50 µM ⁴⁵CaCl₂ and varying pH values. (B) Na⁺/Ca²⁺ antiport with inwardly (pink) and outwardly (green) directed H⁺ gradients. Two sets of liposomes were preloaded with 50 µM ⁴⁵Ca²⁺ and a Na⁺-free buffer with pH set to either 6.3 or 7.3. They were then diluted into their respective reaction buffers containing 100 mM NaCl and 50 µM Ca²⁺ set to pH 7.3 (for pH 6.3 liposomes) and pH 6.3 (for pH 7.3 liposomes). (C) ⁴⁵Ca²⁺/Ca²⁺ exchange under Na⁺-free conditions with inwardly (pink) and outwardly (green) directed H⁺ gradients. Liposomes preloaded with 50 µM ⁴⁵CaCl₂–containing buffer were diluted into a 50 µM CaCl₂–containing buffer. Note that buffers for this experiment were valinomycin-free. A triplicate dataset is averaged (error bars represent SEM).