Figure 4. Ca²⁺- and voltage-dependence of the caffeic acid phenethyl ester-induced increase in BK_Ca-channel activity in inside-out patches of normal human oral keratinocytes. (A) Original current tracings showing the effect of internal Ca²⁺ on the probability of channel openings. The potential was held at +60 mV. "a", "b", and "c" were obtained after the application of 0.1, 1, and 10 µM Ca²⁺, respectively. (B) Bar graph showing the stimulation of BK_Ca channels by caffeic acid phenethyl ester at different concentrations of internal Ca²⁺. The different concentrations of Ca²⁺ in the bath before and during exposure to 10 µM caffeic acid phenethyl ester were applied. Each patch was held at +60 mV. Mean ± SEM (n = 4–6). (C) Voltage dependence of the caffeic acid phenethyl ester- and cinnamyl-3,4-dihydroxy--cyanocinnamate-induced increase in BK_Ca-channel activity of normal human oral keratinocytes. Inside-out patch recordings were performed, and bath medium contained 0.1 µM Ca²⁺. Caffeic acid phenethyl ester or cinnamyl-3,4-dihydroxy--cyanocinnamate was applied to the intracellular surface of the detached patch. The open probability at +100 mV in the control was taken as 1.0. The activation curves of BK_Ca channels in the absence (•) and presence of caffeic acid phenethyl ester (10 µM; ) or cinnamyl-3,4-dihydroxy--cyanocinnamate (10 µM; ) were obtained. Mean ± SEM (n = 4–7).