FIGURE 2.

Ca²⁺ ions coordinated by sites 1 and 2 of CBD1 are not essential for Ca²⁺ regulation. A, examples of giant patch recordings from oocytes expressing the indicated construct. Outward currents were generated by rapidly applying 100 mm Na⁺ into the bath (intracellular surface) with 8 mm Ca²⁺ in the pipette. Representative traces in the presence of three different intracellular Ca²⁺ concentrations are shown (0.13, 1.4, and 20 μm). Neither Na⁺-dependent inactivation nor Ca²⁺ regulation is much affected by mutations at positions 421 or 451. B, Ca²⁺ dependence of outward exchanger current. Values were measured at the peak of the current. Residual current recorded in the absence of regulatory Ca²⁺ has been subtracted. Each point is the average of between two and six experiments. C, summary of the fractional activity values for the WT and the exchanger mutants measured in the presence of the indicated Ca²⁺ concentrations. Fractional activity was measured as the ratio between steady-state and peak currents. Each point is the average of between three and six experiments.