title: Nicotinic acetylcholine receptors containing the α7-like subunit mediate contractions of muscles responsible for space positioning of the snail, Helix pomatia L. tentacle.
abstract: Three recently discovered tentacle muscles are crucial to perform patterned movements of upper tentacles of the terrestrial snail, Helix pomatia. The muscles receive central and peripheral excitatory cholinergic innervation lacking inhibitory innervation. Here, we investigate the pharmacology of acetylcholine (ACh) responses in muscles to determine the properties of the ACh receptor (AChR), the functional availability of which was assessed using isotonic contraction measurement. Using broad spectrum of nicotinic and muscarinic ligands, we provide the evidence that contractions in the muscles are attributable to the activation of nAChRs that contain the α7-like subunit. Contractions could be evoked by nicotine, carbachol, succinylchloride, TMA, the selective α7-nAChR agonist choline chloride, 3-Bromocytisine and PNU-282987, and blocked by nAChR selective antagonists such as mytolon, hexamethonium, succinylchloride, d-tubocurarine, hemicholinium, DMDA (decamethonium), methyllycaconitine, α-Bungarotoxin (αBgTx) and α-Conotoxin IMI. The specific muscarinic agonist oxotremorine and arecoline failed to elicit contractions. Based on these pharmacological properties we conclude that the Na+ and Ca2+ permeable AChRs of the flexor muscle are nicotinic receptors that contain the α7-like subunit. Immunodetection experiments confirmed the presence of α7- or α7-like AChRs in muscle cells, and α4-AChRs in nerves innervating the muscle. These results support the conclusion that the slowly desensitizing αBgTx-sensitive responses obtained from flexor muscles are produced by activation of α7- like AChRs. This is the first demonstration of postsynaptic expression and an obligatory role for a functional α7-like nAChR in the molluscan periphery.
authors.affiliation: Chemical Ecology and Neurobiology Group, Department of Experimental Zoology, Balaton Limnological Institute, MTA Centre for Ecological Research, Tihany, Hungary.
authors.forename: Tibor
authors.initials: T
authors.lastname: Kiss
authors.affiliation: Chemical Ecology and Neurobiology Group, Department of Experimental Zoology, Balaton Limnological Institute, MTA Centre for Ecological Research, Tihany, Hungary.
authors.forename: Nóra
authors.initials: N
authors.lastname: Krajcs
authors.affiliation: Adaptive Neuroetology MTA-CER, National Brain Project Team, Tihany, Hungary.
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Pirger
authors.affiliation: Chemical Ecology and Neurobiology Group, Department of Experimental Zoology, Balaton Limnological Institute, MTA Centre for Ecological Research, Tihany, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Hernádi
mesh_terms: D000818:Animals; D006372:Helix, Snails / Q000502:physiology*; D009068:Movement / Q000187:drug effects / Q000502:physiology; D018721:Muscarinic Agonists / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009132:Muscles / Q000187:drug effects* / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018722:Nicotinic Agonists / Q000494:pharmacology*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism; D064569:alpha7 Nicotinic Acetylcholine Receptor / Q000819:agonists / Q000378:metabolism*
chemical_list: D018721:Muscarinic Agonists; D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor