title: A fungal metabolite asperparaline a strongly and selectively blocks insect nicotinic acetylcholine receptors: the first report on the mode of action.
abstract: Asperparalines produced by Aspergillus japonicus JV-23 induce paralysis in silkworm (Bombyx mori) larvae, but the target underlying insect toxicity remains unknown. In the present study, we have investigated the actions of asperparaline A on ligand-gated ion channels expressed in cultured larval brain neurons of the silkworm using patch-clamp electrophysiology. Bath-application of asperparaline A (10 µM) had no effect on the membrane current, but when delivered for 1 min prior to co-application with 10 µM acetylcholine (ACh), it blocked completely the ACh-induced current that was sensitive to mecamylamine, a nicotinic acetylcholine receptor (nAChR)-selective antaogonist. In contrast, 10 µM asperparaline A was ineffective on the γ-aminobutyric acid- and L-glutamate-induced responses of the Bombyx larval neurons. The fungal alkaloid showed no-use dependency in blocking the ACh-induced response with distinct affinity for the peak and slowly-desensitizing current amplitudes of the response to 10 µM ACh in terms of IC(50) values of 20.2 and 39.6 nM, respectively. Asperparaline A (100 nM) reduced the maximum neuron response to ACh with a minimal shift in EC(50), suggesting that the alkaloid is non-competitive with ACh. In contrast to showing marked blocking action on the insect nAChRs, it exhibited only a weak blocking action on chicken α3β4, α4β2 and α7 nAChRs expressed in Xenopus laevis oocytes, suggesting a high selectivity for insect over certain vertebrate nAChRs.
authors.affiliation: Department of Applied Biological Chemistry, Faculty of Agriculture, Kinki University, Nakamachi, Nara, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Hirata
authors.forename: Saori
authors.initials: S
authors.lastname: Kataoka
authors.forename: Shogo
authors.initials: S
authors.lastname: Furutani
authors.forename: Hideo
authors.initials: H
authors.lastname: Hayashi
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Matsuda
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000470:Alkaloids / Q000378:metabolism* / Q000494:pharmacology*; D000818:Animals; D001230:Aspergillus / Q000378:metabolism*; D012831:Bombyx; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002645:Chickens; D005260:Female; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000378:metabolism* / Q000494:pharmacology*; D009865:Oocytes / Q000378:metabolism; D010879:Piperazines / Q000378:metabolism* / Q000494:pharmacology*; D011978:Receptors, Nicotinic / Q000235:genetics / Q000378:metabolism*; D013141:Spiro Compounds / Q000378:metabolism* / Q000494:pharmacology*; D013379:Substrate Specificity; D014982:Xenopus laevis / Q000235:genetics
chemical_list: D000470:Alkaloids; D018377:Neurotransmitter Agents; D018733:Nicotinic Antagonists; D010879:Piperazines; D011978:Receptors, Nicotinic; D013141:Spiro Compounds; C109708:aspergillimide; D000109:Acetylcholine