Activation of single nicotinic receptor channels from Caenorhabditis elegans muscle.
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 nonmammalian model for the study of the nervous system and a model of parasitic nematodes. Nematode muscle nAChRs are of considerable interest because 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 acetylcholine (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.
Rayes
Diego
D
Instituto de Investigaciones Bioquímicas, Universidad Nacional del Sur-CONICET, Bahía Blanca, Argentina.
Flamini
Marina
M
Hernando
Guillermina
G
Bouzat
Cecilia
C
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D017173:Caenorhabditis elegans / Q000187:drug effects / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics; D015640:Ion Channel Gating / Q000187:drug effects; D007978:Levamisole / Q000494:pharmacology; D009015:Morantel / Q000494:pharmacology; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D050505:Mutant Proteins / Q000378:metabolism; D011715:Pyrantel / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000378:metabolism*
D029742:Caenorhabditis elegans Proteins; D050505:Mutant Proteins; D011978:Receptors, Nicotinic; D007978:Levamisole; D011715:Pyrantel; D009015:Morantel; D000109:Acetylcholine