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.

Cholinesterase inhibitor rivastigmine enhances nerve growth factor-induced neurite outgrowth in PC12 cells via sigma-1 and sigma-2 receptors

“…We next investigated the effect of the AChR antagonists Scop and HEX on the Riv-mediated enhancement of NGF-induced neurite outgrowth. Scop is an mAChR antagonist that inhibits cholinergic transmission in the central nervous system [39], while HEX is an nAChR antagonist [40]. As shown in Fig 5A and 5B, neither Scop (100 μM) nor HEX (100 μM) inhibited NGF-induced neurite outgrowth.…”

Anatomical and physiological background permitting spatial odor sensation in stylommatophoran molluscs

“…PACAP27-like and PAC1R-like immunoreactive nerve fibers were present throughout the muscles. Our experiments demonstrated that PACAP markedly potentiated contractions of the FMs of the upper tentacles evoked by synaptically released or by exogenously applied ACh [49,58]. The effect of PACAP27 enhancing nerve-evoked contractions can be explained by (a) presynaptic mechanisms when PACAP27 binds to specific PAC1Rs leading to the increased release of neurotransmitter, (b) postsynaptic mechanisms, whereby PACAP27 facilitates excitation-contraction coupling of the muscle, or (c) pre-and postsynaptic mechanisms acting together.…”

“…Therefore, we examined in detail the pharmacology of the ACh receptors located at the possible sites of neuromuscular contacts of the FMs. To address this issue, first the pharmacological profile of the muscle AChR was characterized and the receptor subtype identified using molecular tools [49]. The effect of ACh on FMs of the superior tentacles was a slow and consistent tonic, concentration-dependent contraction with no phasic activity.…”

“…The LnAChR A subunit is related to the homo-oligomeric human α7 nAChR and when expressed in oocytes it Acta Biologica Hungarica 67, 2016 is activated by cytosine and nicotine and blocked by αBgTX, αCTX-IMI [94]. However the nAChR in the snail FMs desensitizes slowly and also conducts Na + along with Ca 2+ , suggesting that the receptor is not a homopentamer [49]. In summary, it can be concluded that the slowly desensitizing αBgTx-sensitive responses obtained from FMs were produced by activation of α7-like AChRs.…”

α-Conotoxin ImI-modified polymeric micelles as potential nanocarriers for targeted docetaxel delivery to α7-nAChR overexpressed non-small cell lung cancer

“…ImI is a natural ligand of α7-nAChR with high selectivity, specificity and potency (Ulens et al., 2006 ; Yu et al., 2011 , 2012 ). In addition to its small size and relative ease of synthesis, structural stability and its ability to specifically target α7-nAChR have made it a valuable molecular probe as well as drug lead (Gehrmann et al., 1999 ; Kiss et al., 2014 ). This venom has previously been used in the pharmacological and functional characterization of α7-nAChR, or for inhibiting nicotine action (López et al., 1998 ; Ellison et al., 2004 ; Baxter et al., 2014 ).…”