Fig. 5. Luteolin inhibits calcium-activated Cl^– channel current (I_CaCC), but slightly activates cystic fibrosis transmembrane conductance regulator (CFTR)-mediated Cl^– current (I_CFTR) at a high concentration (> 100 μM) in Calu-3 cells.

(A) Representative traces of I_CaCC, obtained by applying step voltage pulses and inhibiting I_CaCC with various concentrations of luteolin and 2-(4-chloro-2-methylphenoxy)-N-[(2-methoxyphenyl)methylideneamino]-acetamide (Ani9). The holding potential was –60 mV and 4-s step pulses (each 10 mV, –100 to +100 mV) were applied every second. (B) Dose-response curve for luteolin-induced inhibition of I_CaCC. The half-maximal inhibitory concentration (IC₅₀) was 27.91 ± 1.61 μM. (C) Changes (%) in remaining current at +100 mV caused by vitexin, luteolin 7-glucoside (Lu 7-G), apigenin 7-glucoside (Api 7-G), orientin (each at a concentration of 100 μM), and a mixture of the five flavonoid compounds at their respective concentrations in the ethanolic (30%) extract of Spirodela polyrhiza (1 mg/ml). Data are presented as the mean ± standard error of mean. *p < 0.05 compared to the control (n = 4). (D) Representative current (I)/voltage (V) curve for I_CFTR. The curves show the effects of luteolin and CFTRinh-172 (inh-172) on I_CFTR. Luteolin slightly potentiated I_CFTR at a concentration of 100 μM. (E) Normalized current amplitude following the treatment of Calu-3 cells with 100 μM luteolin and inh-172. Data are presented as the mean ± SEM. *p < 0.05 compared to the control (n = 5).