Article

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: 5.71). 09/2008; 22(9):3247-54. DOI:10.1096/fj.08-110502 pp.3247-54
Source: PubMed

ABSTRACT 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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    Article: Levamisole-activated single-channel currents from muscle of the nematode parasite Ascaris suum.
    S J Robertson, R J Martin
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    ABSTRACT: 1. The patch-clamp technique was used to examine levamisole-activated channels in muscle vesicles from Ascaris suum. Cell-attached and isolated inside-out patches were used. 2. Levamisole (1-90 microM), applied to the extracellular surface, activated channels which had apparent mean open-times in the range 0.80-2.85 ms and linear I/V relationships with conductances in the range 19-46 pS. Ion-replacement experiments showed the channels to be cation selective. 3. The kinetics of the channels were analysed. Generally open- and closed-time distributions were best fitted by two, and three exponentials respectively, indicating the presence of at least two open states and at least three closed states. The distributions of burst-times were best-fitted by two exponentials. 4. Channel open- and burst-times were voltage-sensitive: at low levamisole concentrations (1-10 microM), they increased with hyperpolarization. At higher concentrations of levamisole (30 microM and 90 microM) flickering channel-block was observed at hyperpolarized potentials. Using a simple channel-block model, values for the blocking dissociation constant, KB were determined as 123 microM at -50 mV, 46 microM at -75 mV and 9.4 microM at -100 mV. 5. At the higher concentration of levamisole (30 microM and 90 microM) long closed-times separating 'clusters' of bursts were observed, at both hyperpolarized and depolarized membrane potentials and this was interpreted as desensitization.
    British Journal of Pharmacology 02/1993; 108(1):170-8. · 4.41 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

Keywords

antinematodal drug
 
C. elegans
 
Caenorhabditis elegans
 
currents
 
genetic level
 
lev-1 mutant C. elegans
 
LEV-1 mutants
 
LEV-10 knockouts
 
levamisole resistance
 
levamisole-activated whole muscle cell currents
 
model organism
 
nAChR channel currents
 
nAChRs aggregate
 
neuromuscular transmission
 
nicotinic acetylcholine receptor
 
nicotinic anthelmintic drug levamisole
 
single-channel level
 
single-channel recording
 
situ recordings
 
wild-type adults