Abstract
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.
Footnotes
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This work was supported by grants from Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional del Sur, Fondo para la Investigación Científica y Tecnológica, and a fellowship from John Simon Guggenheim Memorial Foundation (to C.B.).
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Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
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doi:10.1124/mol.106.033514.
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ABBREVIATIONS: nAChR, nicotinic acetylcholine receptor; ACh, acetylcholine; L-AChR, levamisole-sensitive nicotinic acetylcholine receptor; N-AChR, levamisole-insensitive and nicotine-sensitive acetylcholine receptor; PCR, polymerase chain reaction; RT-PCR, reverse transcription-polymerase chain reaction; DHβE, dihydro-β-erythroidine.
- Received December 14, 2006.
- Accepted February 21, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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