Activation of Single Nicotinic Receptor Channels from Caenorhabditis elegans Muscle

DH RAYES; M FLAMINI; G HERNANDO; C BOUZAT

MOLECULAR PHARMACOLOGY

American Society for Pharmacology and Experimental Therapeutics

Año: 2007 vol. 71 p. 1407 - 1415

0026-895X

Nicotinic acetylcholine receptors (nAChRs) are pentameric neurotransmitter-gated ion channels that mediate synaptic transmission throughout the nervous system in vertebrates and invertebrates. Caenorhabditis elegans is a non-mammalian model for the study of the nervous system as well as a model of parasitic nematodes. Nematode muscle nAChRs are of considerable interest as they are targets for anthelmintic drugs. We show single-channel activity of C. elegans muscle nAChRs for the first time. Our results reveal that in the L1 larval stage ACh activates mainly a levamisole-sensitive nAChR (L-AChR). A single population of 39 pS channels, which are 5-fold more sensitive to levamisole than ACh, is detected. In contrast to mammalian nAChRs, open durations are longer for levamisole than for ACh. Studies in mutant strains reveal that UNC-38, UNC-63 and UNC-29 subunits are assembled into a single L-AChR in the L1 stage and that these subunits are irreplaceable, suggesting that they are vital for receptor function throughout development. Recordings from a strain mutated in the LEV-1 subunit show a main population of channels with lower conductance (26 pS), prolonged open durations, and reduced sensitivity to levamisole. Thus, although LEV-1 is preferentially incorporated into native L-AChRs, receptors lacking this subunit can still function. No single-channel activity from levamisole-insensitive nAChRs is detected. Thus, during neuromuscular transmission in C. elegans the majority of ACh-activated current flows through L-AChRs. This study contributes to the understanding of the molecular mechanisms underlying functional diversity of the nAChR family and offers an excellent strategy to test novel antiparasitic drugs.