title: Block of nicotinic acetylcholine receptors by philanthotoxins is strongly dependent on their subunit composition.
abstract: Philanthotoxin-433 (PhTX-433) is an active component of the venom from the Egyptian digger wasp, Philanthus triangulum. PhTX-433 inhibits several excitatory ligand-gated ion channels, and to improve selectivity two synthetic analogues, PhTX-343 and PhTX-12, were developed. Previous work showed a 22-fold selectivity of PhTX-12 over PhTX-343 for embryonic muscle-type nicotinic acetylcholine receptors (nAChRs) in TE671 cells. We investigated their inhibition of different neuronal nAChR subunit combinations as well as of embryonic muscle receptors expressed in Xenopus oocytes. Whole-cell currents in response to application of acetylcholine alone or co-applied with PhTX analogue were studied by using two-electrode voltage-clamp. α3β4 nAChRs were most sensitive to PhTX-343 (IC50= 12 nM at -80 mV) with α4β4, α4β2, α3β2, α7 and α1β1γδ being 5, 26, 114, 422 and 992 times less sensitive. In contrast α1β1γδ was most sensitive to PhTX-12 along with α3β4 (IC50values of 100 nM) with α4β4, α4β2, α3β2 and α7 being 3, 3, 26 and 49 times less sensitive. PhTX-343 inhibition was strongly voltage-dependent for all subunit combinations except α7, whereas this was not the case for PhTX-12 for which weak voltage dependence was observed. We conclude that PhTX-343 mainly acts as an open-channel blocker of nAChRs with strong subtype selectivity.
authors.affiliation: School of Life Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
authors.forename: Hamid S
authors.initials: HS
authors.lastname: Kachel
authors.affiliation: School of Life Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
authors.forename: Rohit N
authors.initials: RN
authors.lastname: Patel
authors.affiliation: Department of Drug Design and Pharmacology, University of Copenhagen, Jagtvej 162, DK-2100 Copenhagen, Denmark.
authors.forename: Henrik
authors.initials: H
authors.lastname: Franzyk
authors.affiliation: School of Life Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
authors.forename: Ian R
authors.initials: IR
authors.lastname: Mellor
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D004534:Egypt; D005260:Female; D006801:Humans; D051379:Mice; D018733:Nicotinic Antagonists / Q000494:pharmacology*; D009865:Oocytes / Q000378:metabolism; D010636:Phenols / Q000494:pharmacology*; D011073:Polyamines / Q000494:pharmacology*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000494:pharmacology; D014982:Xenopus laevis / Q000378:metabolism
chemical_list: D018733:Nicotinic Antagonists; D010636:Phenols; D011073:Polyamines; D011978:Receptors, Nicotinic; C403530:nicotinic receptor alpha3beta4; C405122:phTX 12; C074003:philanthotoxin 343; D014443:Tyrosine; C034092:delta-philanthotoxin; D000109:Acetylcholine