Characterization of the antiparasitic bephenium as an agonist of Caenorhabditis elegans levamisole-sensitive nicotinic receptors

HERNANDO, G.S.; BOUZAT, C.; TURANI, O.

Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

Sociedad Argentina de Biofísica

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that are involved in neuromuscular transmission. Nematode muscle nAChRs are of clinical importance because they are targets of anthelmintic drugs. The muscle nAChRs of nematode parasites fall into three pharmacological classes that are activated by levamisole (L-type), nicotine (N-type) and bephenium (B-type). In Caenorhabditis elegans muscle, only the N-AChR and L-AChR types have been described. We here determined the behavioral (by paralysis assays) and molecular effects (by patch clamp recordings) of bephenium, which is used for infections caused by intestinal helminths, on C. elegans. As in parasites, bephenium produced spastic paralysis. Strains lacking accessory (LEV-8) or essential (UNC-38) subunits of the L-AChR showed partial or full resistance to bephenium, respectively, thus indicating that the L-AChR is the drug target. To decipher its molecular actions, we performed single-channel recordings from isolated larvae L1 and L3 cells. Bephenium (1-100 μM) activated L-AChRs of both developmental stages, eliciting channel openings of 3.6 pA (-100 mV) with mean durations of 0.26±0.03 ms. Analysis of the channel properties as a function of drug concentration showed that at higher concentration it also acts as an open-channel blocker. To determine the selectivity of bephenium among muscle nAChRs, we studied its action at the mammalian muscle nAChR. Bephenium (10-100 μM) elicited single-channel currents, indicating that it is also an agonist of the mammalian muscle nAChR. However, when compared to ACh, openings were significantly briefer and activation episodes were not observed, indicating that bephenium is a very low efficacious agonist of this nAChR. Overall, we revealed that bephenium is an agonist of the L-AChR of the free-living nematode C. elegans, which is used as a parasite model, and a very low-efficacy agonist of mammalian nAChRs, at which it might mediate adverse effects.Keywords: nicotinic receptor, ion-channel, patch-clamp, Caenorhabditis elegans.