Figure 2.

Functional reconstitution of NCX_Mj. (A) ⁴⁵Ca²⁺ uptake into protein-free (gray) or NCX_Mj-containing (orange) liposomes in the presence of an outwardly directed Na⁺ gradient. The liposomes were preloaded with 100 mM NaCl and 1 µM ⁴⁵Ca²⁺, set with EGTA, and external buffers contained 5 µM ⁴⁵CaCl₂ and were nominally Na⁺-free. The presence of valinomycin and K⁺ dissipated any transmembrane voltage generated by the transport process. Valinomycin and K⁺ were used in all experiments, unless specifically noted otherwise. (B) Initial rates of ⁴⁵Ca²⁺ transport as a function of external Na⁺ concentration. The liposomes were preloaded with buffer containing 25 mM NaCl and 100 µM ⁴⁵CaCl₂. External buffers contained 25 µM ⁴⁵CaCl₂ and varying amounts of NaCl. A triplicate dataset is averaged (error bars represent SEM). This experiment was reproduced on two separate occasions.