Muscle Nicotinic Receptors in Nematodes

RAYES, D; HERNANDO, G; BERGÉ I.; BOUZAT, C.

Huerta Grande, Córdoba

Conferencia; First Joint Meeting of the Argentine Society for Neuroscience (SAN) and the Argentine Workshop in Neurosciences (TAN); 2009

Sociedad Argentina de Investigación en Neurociencias

Nicotinic acetylcholine receptors (AChRs) are pentameric neurotransmitter gated ion channels that mediate synaptic transmision in both vertebrates and invertebrates. Caenorhabditis elegans is a model of parasitic nematodes and has emerged as a model for studying the nervous system. C. elegans has one of the largest AChR subunit families known. Nevertheless, the composition and roles of AChRs in C.elegans muscle remain to be resolved. Nematode muscle AChR are of interest as they are targets for anthelmintic drugs.By using single-channel and whole cell recordings of in vitro differentiated C.elegans muscle cells, we analyzed the activation properties of nematode levamisole sensitive AChR (L-AChR). Our results revealed that the widely used nematocide drugs, levamisole, pyrantel and morantel, are agonists 5 to 10-fold more potent that the neurotransmitter ACh. We demonstrated that UNC-63, UNC-38, UNC-29, LEV-1 and LEV-8 subunits assemble into a single L-AChR, being the first three essential for receptor function throughout development. Although LEV-1 is preferentially incorporated into L-AChRs, the lack of this subunit allows the expression of functional receptors with different kinetics. In addition, we found that LEV-8 also acts as an accessory subunit, and plays a key role in the desensitizationof L-AChRs.We studied a strain with impaired lcomotion in which the UNC-63 subunit carries a mutation (C151Y) that mimics the one observed in a congenital myasthenic syndrome (CMS) patient. This mutation reduces expression, the channel open probability and the opening rate of L-AChRs similar to the activation profile reported for the human CMSs. Moreover, drugs used for treatment of these disorders partially rescue the phenotype of the mutant worms. Therefore, we validate this strain as an invertebrate model for human CMS.These studies contribute to the understanding of molecular mechanisms underlying diversity of nAChRs and offer an excellent strategy for screening novel therapeutics agents.