Fig. 1. Plot of measured calcium K_d as a function of pH for the fluorescent calcium probes furaDx () and OGBDx ([UNK]). The solid line represents the predicted K_d of BAPTA using the constants measured by Tsien (Tsien, 1980) and the methods of Bers et. al. (Bers et al., 1994) to correct for temperature, ionic strength and pH. All measurements were performed at 22°C with constant ionic strength (0.130 M) and variable pH (4-7.2) in Hepes/MES pH buffers containing 1 mM Mg²⁺.