Basic properties of BK channels in POPE/POPS 3:1 (wt/wt) bilayers. (A) Original records of cbv1 channel activity obtained at 0.3, 10, and 50 μM Ca²⁺ at the cytosolic side of the control sterol-free POPE/POPS 3:1 (wt/wt) and 33 mol% cholesterol-containing lipid bilayer. Records show a progressive increase in Po as [Ca²⁺]_i is increased. Channel openings are shown as upward deflections; arrows indicate the baseline. The membrane potential for each recording was set to 0 mV. (B) A voltage (V)–Po plot obtained after the incorporation of cbv1 protein into control (n = 5) versus cholesterol-containing (n = 7) bilayers underscores that cholesterol presence does not alter the voltage dependence of cbv1 channel gating. Po values at each voltage in cholesterol-containing versus cholesterol-free (control) bilayers were normalized to their corresponding maximum (Po_Max in cholesterol-containing bilayer, ≈0.7; Po_Max in control bilayer, ≈0.9). (C) Cbv1 channel unitary current amplitude (i)–voltage (V) relationships from records obtained in 300/30 mM K⁺ render unitary (slope) conductances of ≈340 and ≈330 pS for control (n = 5) and cholesterol-containing (n = 7) bilayers; these values are characteristic of BK channels. For B and C, data were obtained at [Ca²⁺]_i = 10 μM. Curve fitting was performed using Origin7 (OriginLab).