Figure 1. Single-channel currents from a hair cell BK channel in the inside-out patch configuration.
Single-channel currents are shown at three holding voltages for a patch exposed to 1 (A) and 8.3 μm[Ca2+] (B). In all cases, channel opening is upward. C, open probability (Po) was fitted with a single Boltzmann function (continuous lines) for each calcium concentration (indicated by numbers adjacent to curves, in μm). D, half-activating voltage (V1/2)from the Boltzmann fits is shown and fitted across the tested calcium concentrations using a logarithmic relationship predicted by a simple two-state model. The calcium concentration required for half-activation at 0 mV, KD(0), was determined to be 3.2 μm. E, current amplitude is plotted against holding voltage. Data from four separate calcium conditions are included in this plot. The curve fit (dashed line) indicates a single-channel conductance of 302 pS. Data in A-E are all from the same patch, taken from a hair cell at 36 % distance from the apical end.