Muscle Nicotinic Receptors in Nematodes

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

Los Cocos, Córdoba, Argentina

Congreso; First Join Meeting of the Argentine Society for Neurosciences (SAN) and the Argentine Workshop; 2009

SAN TAN

Nicotinic acetylcholine receptors (AChRs) are pentameric neurotransmitter-gated ion channels that mediate fast synaptic transmission throughout the nervous system in both vertebrates and invertebrates. Nematode muscle AChRs are targets for anthelmintic drugs, which produce spastic paralysis and ultimately death. We here explore at the single-channel level activation by ACh and anthelmintics of nematode AChRs from Caenorhabditis elegans, which is the model for the study of parasitic nematodes. By using a primary culture method that allows differentiation of C. elegans embryonic cells into larva 1 (L1) muscle cells in vitro, we show for the first time single-channel currents from AChRs. Our results show that in the L1 stage ACh activates mainly a levamisole-sensitive AChR. This receptor exhibits a conductance of 39 pS, which is significantly lower than that of mammalian AChRs. In contrast to mammalian AChRs, there are not significant differences in the activation kinetics between ACh and levamisole. Moreover, the activation potency is greater for levamisole than for ACh. Recordings from mutant strains reveal that UNC-63, UNC-38 and UNC-29 are essential for channel activity. Recordings from strains carrying a missense mutation in the LEV-1 subunit, which has been characterized as a non-alpha- AChR subunit, show a reduction in the frequency of channel openings and in the potency for both agonists. Moreover, channels show lower conductance and prolonged open durations. The analysis indicates that channel activity probably arises from channels lacking LEV-1, suggesting that this subunit can be replaced by other in the pentameric AChR. Thus, LEV-1 plays a key role in nematode AChR function as it is preferentially incorporated into functional AChRs. Although the mRNA for the levamisole-insensitive receptor ACR-16 is detected in the L1 developmental stage, no single-channel activity from N-AChRs is observed in cell-attached patches. In conclusion, during neuromuscular transmission in C. elegansthe majority of ACh-activated current flows through L-AChRs, whose activation kinetics are greatly different from those of mammals. This differential activation by anthelmintic drugs between species can be exploited therapeutically.