Functional Role of LEV-8 subunit of Levamisole-Sensitive Nematode Muscle Nicotinic Receptors

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

Bahía Blanca, Argentina

Workshop; Workshop Neuronal Communication: from structure to physiology; 2008

Sociedad Argentina de Investigación en Neurociencias

Caenorhabditis elegans is a free-living nematode and a representative member of a large phylum that includes many parasitic members. Nematode nicotinic acetylcholine receptors (AChRs) are pentameric neurotransmitter-gated ion channels that mediate fast synaptic transmission throughout the nervous system. The muscle levamisole-sensitive AChR (L-AChR) is the target of anthelmintic drugs, such as levamisole, which act as potent agonists. They produce spastic paralysis and ultimately death of the worm. By using a primary culture method that allows differentiation of C.elegans embryonic cells into larva 1 muscle cells in vitro we have reported the first single-channel characterization of single-channel currents from L-AChRs, and demonstrated that UNC-63, UNC-38 and UNC-29 subunits are essential for channel activity, whereas LEV-1 subunit is an accessory subunit . We here explored the functional role of LEV-8, an alphatype subunit that when mutated confers partial resistance to the paralytic effects of levamisole without significant effects in worm motility. Single-channel recordings performed on muscle cells isolated from the null mutant strain lev-8(x-15) show ACh and levamisole-activated channels with a conductance of 39.6 ± 4.0 pS, similar to that recorded from the wild-type strain. The mean open time of the L-AChR channels for both agonists are 3.9 and 1.5 fold more prolonged than those of the wild-type respectively.The frequency of channel openings is markedly reduced with respect to that of wild type strains. Detailed analysis of activation episodes reveals that desensitization is enhanced in the mutant strain. Thus, the lev-8 subunit may have a role in determining the rate of desensitization of the pentameric L-AChR. This study contributes to the elucidation of the stoichiometry of nematode muscle L-AChRs and to the understanding of how nematodes develop resistance to anthelmintic drugs.