Macroscopic currents recorded after cbv1+β1–4 subunit expression in Xenopus oocytes show characteristic features of BK currents. (A) Representative current records from I/O macropatches expressing different BK channel subunit combinations (cbv1±β1/wt β2/β2-IR/β3/β4; 10 µM Ca²⁺_i). Currents were evoked by 100 ms-long (except for cbv1+wt β2; 600 ms-long; 3 µM Ca²⁺_i), 10-mV depolarizing steps from −150 to 150 mV, with a holding potential set to −80 mV. cbv1+wt β2 channels are characterized by fast inactivation. (B) V_0.5 versus [Ca²⁺]_i plot underscores that β subunit types differentially modulate the apparent Ca²⁺_i sensitivity of the channel complex. (C and D) Bar graphs show averaged activation (τ_act) and deactivation (τ_deact) time constants, respectively, obtained at V_max with Ca²⁺_i = 10 µM. Mean V_max (mV) values for different constructs were (mean ± SEM) cbv1 = 117 ± 8.2; cbv1+β1 = 55 ± 14; cbv1+β2-IR = 40 ± 3.3; cbv1+β3 = 80 ± 17; cbv1+β4 = 130 ± 8. τ_deact was estimated from tail currents after stepping down to −80 mV from V_max. n = 4–8; *, different from cbv1 (P < 0.05); #, different from cbv1+β1 (P < 0.05). Data are expressed as mean ± SEM.