Figure 6.

Electrogenic nature of Na⁺/Ca²⁺ antiport. (A) Na⁺/Ca²⁺ antiport in the presence (green) or absence (gray) of valinomycin. Liposomes were preloaded with 100 mM NaCl buffer and diluted into a reaction buffer containing 50 µM ⁴⁵CaCl₂. This experiment was reproduced on three separate occasions. (B) Na⁺/Ca²⁺ antiport with inside-positive (green) and inside-negative (gray) membrane potentials. Liposomes preloaded with 25 mM NaCl and 50 µM ⁴⁵CaCl₂ were diluted into a reaction buffer containing 25 mM NaCl and 25 µM ⁴⁵CaCl₂. The membrane potential was set with 10 mM KCl internally, and either 100 mM KCl (green) or 0.5 mM (gray) KCl externally. Analogous measurements using protein-free liposomes are also shown (black). A triplicate dataset is averaged (error bars represent SEM).