Figure 3. Tannic acid (TA) counteracts SaSMase C and SMase D suppression of CFTR current.
(A) Correlation plot of Z scores (raw scores minus the mean of the population, divided by the standard deviations of individual compounds) of individual compounds tested in two repeated screens; 27 compounds with higher Z scores are colored orange. (B) Percentage SaSMase C suppression of CFTR currents in the presence of 27 tested compounds, each at 10 µM. (C) Time course of normalized CFTR currents at 50 mV without or with 10 µM tannic acid (TA) present in the bath; arrow indicates addition of SaSMase C (0.6 ng/µl). (D) and (E) Time courses of normalized CFTR currents at 50 mV without and with 100 or 200 nM (D) or 300 nM (E) tannic acid present in the bath; arrow indicates addition of SaSMase C (D) and SMase D (E) (mean ± s.e.m, n = 3–5). (F) Apparent activities of SaSMase C (1 and 2) or SMase D (0.6 ng/μl) (3) plotted against the concentration of tannic acid, where the activities are expressed as half-time of the time course of sphingomyelin hydrolysis (1) or CFTR inhibition (2 and 3), which were obtained by the Amplex red assay (1) or by electrophysiological recordings (2 and 3). The half-time values were normalized to the corresponding ones obtained in the presence of relevant enzymes and the absence of tannic acid.