Figure 2.

Ca²⁺-dependent regulation of NCX and CALX. (A) Schematic representation of NCX1 currents upon the application of intracellular Na⁺ to initiate the exchange reaction in the presence of varying [Ca²⁺]_i. Na⁺ applications initially activates NCX1, followed by a slow decrease in exchange current representing Na⁺-dependent inactivation. Higher [Ca²⁺]_i results in larger peak currents and reduced Na⁺-dependent inactivation, as reflected by the higher steady-state current in the presence of 10 μM [Ca²⁺]_i. Binding of Ca²⁺ ions (green spheres) to the Ca3-Ca4 sites of CBD1 (yellow sticks) results in peak-current activation, whereas the binding of one Ca²⁺ ion to the CaI site of CBD2 (red sticks) results in steady-state current activation. (B) Schematic representation of CALX1.1 currents upon the application of intracellular Na⁺ to initiate the exchange reaction in the presence of varying amounts of [Ca²⁺]_i. Na⁺ application initially activates NCX, followed by a slow decrease in exchange current representing Na⁺-dependent inactivation. Higher [Ca²⁺]_i results in smaller peak currents and increased Na⁺-dependent inactivation, as reflected by the smaller steady-state current in the presence of 10 μM [Ca²⁺]_i.