Characterization of the effects of selected LC on the pumping rate. (A) Time-dependent effect of the amyloidogenic cardiotoxic protein (H6-BJ) and the nonamyloidogenic one (MM2-BJ) on the pumping rate of worms. Proteins, in 10 mM PBS (pH 7.4), were administered to worms at 100 µg/mL. Control worms received vehicle alone (Vehicle). Nematodes (100 worms/100 µL) were incubated with LCs for 2 hours in the absence of OP50 E coli and then plated on NGM plates seeded with bacteria. The pharyngeal pumping was scored at different times after plating (2-48 hours). Data are expressed as the mean ± standard error (SE) (n = 20 worms/group). *P < .01 vs vehicle and MM2-BJ, Student t test. (B) Dose-response effect of 1 to 200 µg/mL of H6-BJ and MM2-BJ. Mean ± SE (n = 40 worms/group). *P < .01 vs MM2-BJ, Student t test. (C) Effect of H6-BJ on the feeding behavior. Feeding assay was performed by monitoring the ability of worms to ingest multifluorescent beads. H6-BJ protein (100 µg/mL) in 10 mM PBS (pH 7.4) or vehicle alone (Vehicle) were administered to worms. Representative images, obtained from the overlay of a contrast phase and epifluorescence, indicated the presence of fluorescent beads (black arrows) in the pharynx of control worms, but not in those fed H6-BJ protein. (D) Dose-response effect of 1 to 200 µg/mL of recombinant cardiotoxic (H3-r) or noncardiotoxic (K3-r) proteins. Mean ± SE (n = 30 worms/group). *P < .01 vs K3-r, Student t test. (E) Comparison of the dose-response curves obtained for H3-r and H6-BJ proteins. IC₅₀ values ± standard deviation were reported. The 2 proteins, at 100 µg/mL, similarly inhibited the pumping rate of worms (from 235.0 ± 3.6 pumps/min of vehicle to 177.6 ± 3.2 pumps/min and 170.4 ± 2.8 pumps/min for H6-BJ and H3-r, respectively).