Ethanol activates β1-containing BK channels at submicromolar (0.3 µM) Ca²⁺_i, while causing strong inhibition at higher (100 µM) Ca²⁺_i. (A) Macroscopic current recordings from I/O patches obtained at 0.3 and 100 µM Ca²⁺_i in the absence or presence of 50 mM ethanol after cbv1+β1 expression in Xenopus oocytes. (B and C) Ethanol shifts the G/G_max-V plot to the left at 0.3 µM Ca²⁺_i, indicating BK current potentiation (B), while shifting the plot to the right at 100 µM Ca²⁺_i, indicating inhibition (C). (D) β1 subunits set the activation to inhibition crossover of ethanol responses at ≈3 µM Ca²⁺_i. (E) Bar graph representing ethanol-induced change in V_0.5 values from pre-ethanol application obtained at 0.3 µM and 100 µM Ca²⁺_i. n = 5–8; each patch was excised from a different cell. *, different from control (P < 0.05); **, different from control (P < 0.01). Data are expressed as mean ± SEM.