(**a**–**b**) Cartoons of the predicted topology of α-, β2- and γ1-subunits. The basic topology of β2- and γ1-subunits are shared with other members of their respective subunit families. (**c**) Schematic of deduced position of α- and β1-subunit TM segments in a BK channel complex viewed at the extracellular face. Grey, pink and blue ellipses highlight voltage sensor domain (VSD), pore domain (PD) and β-subunit TMs, respectively. (**d**–**g**) Typical currents arising from (co)expression of BK subunits in oocytes: α alone, α+γ1, α+β2, or α+β2+γ1, respectively, at 0 (left) or 10 μM intracellular [Ca^{2+}] (right); left and right currents were from the same patch using the same voltage protocol (depicted for each case). (**h**–**i**) Comparison among activation curves (*G*–*V*) at 0 Ca^{2+} or 10 μM of Ca^{2+}, respectively, generated from sets of experiments as in panels (**d**–**g**). Notice the overlap between activation curves at 0 Ca^{2+} of α+γ1 and α+β2+γ1. *G*–*V* fits to single Boltzmann distributions yielded the following parameters: At 0 Ca^{2+}, α-alone (*V*_{h}=193±6 mV, *z*=0.7±0.02 *e*_{0}, *n*=5); α+β2ΔNt (*V*_{h}=182±4 mV, *z*=0.7±0.03 *e*_{0}, *n*=5) ; α+γ1 (*V*_{h}=29.0±4.7 mV, *z*=1.3±0.08 *e*_{0}, *n*=7); α+β2+γ1 (*V*_{h}=28.9±3.4 mV, *z*=0.9±0.04 *e*_{0}, *n*=9). At 10 μM of Ca^{2+}, α-alone (*V*_{h} =22.6±3 mV, *z*=1.4±0.12 *e*_{0}, *n*=5); α+β2ΔNt (*V*_{h}=−9.2±4.4 mV, *z*=1.6±0.87 *e*_{0,} *n*=5); α+γ1 (*V*_{h}=−95.1±3.9 mV, *z*=1.4±0.05 *e*_{0}, *n*=8). (**j**) Averages of *τ*_{inact} at voltages up to +180 for α+β2+γ1 at 0 Ca^{2+} (*n*=9) and α+β2 at 10 Ca^{2+} (*n*=6), respectively. All errors are s.e.m.

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