Figure 5.

The Ca²⁺ binding affinities of the Ca²⁺ bowl site at −80 mV. (A) Inward K⁺ currents recorded from mutant ΔEΔR at −80 mV and filtered at 10 kHz from a macropatch exposed to the indicated [Ca²⁺] demonstrate that Popen increases in a Ca²⁺-dependent manner when voltage is constant. The corresponding all-point amplitude histograms are plotted in B on a semi-log scale and were constructed from 30-s recordings as in Fig. 2. The dose–response relation for the effect of [Ca²⁺] on Popen (left axis) and NPopen/NPopen_min (right axis) at negative voltage (−80 mV) is shown in C. Each point represents the average of between 6 and 11 patches at each [Ca²⁺] tested. Log (NPopen/NPopen_min) spans the entire [Ca²⁺] range and is fit (solid line) by Eq. 6 yielding values of K_O = 0.88 μM and K_C = 3.13 μM. Error bars represent SEM.