Figure 5
Effects of chemicals on ATPase activities of recombinant zebrafish Abcb4. Compounds were tested for stimulation (open squares) of Abcb4 ATPase and inhibition of the verapamil-stimulated Abcb4 ATPase activities (closed circles). Tested compounds were verapamil (A), calcein-am (B), rhodamine B (C), cyclosporin A (D), MK571 (E), PSC833 (F), vinblastine (G), vincristine (H), doxorubicin (I), tonalide (J), galaxolide (K) and phenanthrene (L). Values are means +/− SEM from three to four independent experiments. Means and SEM ranges of the baseline (bl) and with 40 μM verapamil maximally stimulated ATPase activities (ms) are indicated as horizontal dotted lines. Regression curves for ATPase stimulation were fitted using a modified Michaelis-Menten equation {VS = (K1K2V0 + K2V1S + V2S2)/(K1K2 + K2S + S2) [28, 29]}; regression curves for inhibition of the stimulated ATPase activities were fitted to a modified version of this equation describing the descending part of the curve {VS = V1 + ((V2X)/(K2 + X))}. Statistically significant effects on ATPase stimulation or inhibition of stimulated ATPase activities were identified by comparison of data with baseline and maximally stimulated ATPase activities, respectively, using one-way analysis of variance (ANOVA), followed by Dunnett’s test and are indicated by asterisks (*: P <0.05) below the baseline line (different from baseline activity - significant stimulation) or above the line of maximal stimulation (different from the maximally stimulated activity - significant inhibition).