Activation of single nicotinic receptor channels from Caenorhabditis elegans muscle

DH RAYES; M FLAMINI; G HERNANDO; CECILIA BEATRIZ BOUZAT

Baltimore

Congreso; 51st Annual Meeting Biophysical Society; 2007

Biophysical Society

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 AChRs from Caenorhabditis elegans, which is a model for the study of parasitic nematodes. We show for the first time single AChR channels from in vitro differentiated muscle cells. Our results show that in the L1 stage ACh activates mainly a levamisole-sensitive AChR (L-AChR). A single homogeneous population of 39 pS channels, which are 5-fold more sensitive to levamisole than ACh, is observed. In contrast to mammalian AChRs, open durations are longer for levamisole than for ACh. Recordings from mutant strains confirm that UNC-63, UNC-38 and UNC-29 are essential for channel activity. A missense mutation in the LEV-1 subunit leads to a reduction in the frequency of openings and in the potency for levamisole-activation. Moreover, recordings show a main population of channels with lower conductance (26 pS) and prolonged open durations. Thus, although LEV-1 is preferentially incorporated into native L-AChRs, receptors lacking this subunit can still function. Although mRNA for ACR-16, which forms the levamisole-insensitive receptor (N-AChR), is detected in the L1 developmental stage, no channel activity from N-AChRs is observed in cell-attached patches. In conclusion, during neuromuscular transmission in C. elegans the majority of ACh-activated current flows through L-AChRs, whose activation kinetics is greatly different from that of mammalian muscle receptors. Studies at the single-channel level will be useful to test the action of novel antiparasitic agents.