Levamisole resistance resolved at the single-channel level in Caenorhabditis elegans

Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA.
The FASEB Journal (Impact Factor: 5.04). 09/2008; 22(9):3247-54. DOI: 10.1096/fj.08-110502
Source: PubMed


Sydney Brenner promoted Caenorhabditis elegans as a model organism, and subsequent investigations pursued resistance to the nicotinic anthelmintic drug levamisole in C. elegans at a genetic level. These studies have advanced our understanding of genes associated with neuromuscular transmission and resistance to the antinematodal drug. In lev-8 and lev-1 mutant C. elegans, levamisole resistance is associated with reductions in levamisole-activated whole muscle cell currents. Although lev-8 and lev-1 are known to code for nicotinic acetylcholine receptor (nAChR) subunits, an explanation for why these currents get smaller is not available. In wild-type adults, nAChRs aggregate at neuromuscular junctions and are not accessible for single-channel recording. Here we describe a use of LEV-10 knockouts, in which aggregation is lost, to make in situ recordings of nAChR channel currents. Our observations provide an explanation for levamisole resistance produced by LEV-8 and LEV-1 mutants at the single-channel level.

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    • "Using this stringent approach, we predicted 260 druggable proteins in H. contortus (see Additional file 1, Table S17), of which 106 had ligands fulfilling the Lipinsky rule of five [80] (Table 3). Conspicuous among these were 17 channels or transporters, which represent protein classes known to be targets for anthelmintics, including macrocyclic lactones, levamisoles, and AADs [7,81,82], and other candidates including 27 kinases, 7 TFs, and 4 phosphatases known to be specific targets for norcantharidin analogues [77]. This list of prioritized target candidates could be tested for anti-nematodal effects in larval development assays or directly in experimental sheep, and should enable rational anthelmintic design. "
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    • "In addition to these three channel populations, in the strongyle species O. dentatum belonging to the same phylogenetic clade as H. contortus and C. elegans, a forth levamisole activated AChR subtype harboring a conductance of 40 pS has also been observed (Robertson et al. 1999). In sharp contrast, levamisole application revealed only one conductance of approximately 30 pS in C. elegans (Qian et al. 2008). Therefore, it is tempting to hypothesize that L-AChR diversity could be associated with parasitic life-style. "
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    • "While few single channel studies have been conducted on dissected body wall muscles, this approach has been applied to study large-conductance, calciumactivated potassium channels with the excised patch-clamp technique (Carre- Pierrat et al., 2006). Because body wall muscle receptors are clustered at synapses that localize to inaccessible muscle arms, mutants that disrupt the synaptic localization of the levamisole-sensitive ACh receptor have been used to study their single channel properties (Qian et al., 2008) (Fig. 9B2, top). No such de-clustering mutants are yet available to study the nicotine-sensitive receptor or the GABA receptor. "
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