title: A novel muscarinic receptor-independent mechanism of KCNQ2/3 potassium channel blockade by Oxotremorine-M.
abstract: Inhibition of KCNQ (Kv7) potassium channels by activation of muscarinic acetylcholine receptors has been well established, and the ion currents through these channels have been long known as M-currents. We found that this cross-talk can be reconstituted in Xenopus oocytes by co-transfection of human recombinant muscarinic M1 receptors and KCNQ2/3 potassium channels. Application of the muscarinic acetylcholine receptor agonist Oxotremorine-methiodide (Oxo-M) between voltage pulses to activate KCNQ2/3 channels caused inhibition of the subsequent KCNQ2/3 responses. This effect of Oxo-M was blocked by the muscarinic acetylcholine receptor antagonist atropine. We also found that KCNQ2/3 currents were inhibited when Oxo-M was applied during an ongoing KCNQ2/3 response, an effect that was not blocked by atropine, suggesting that Oxo-M inhibits KCNQ2/3 channels directly. Indeed, also in oocytes that were transfected with only KCNQ2/3 channels, but not with muscarinic M1 receptors, Oxo-M inhibited the KCNQ2/3 response. These results show that besides the usual muscarinic acetylcholine receptor-mediated inhibition, Oxo-M also inhibits KCNQ2/3 channels by a direct mechanism. We subsequently tested xanomeline, which is a chemically distinct muscarinic acetylcholine receptor agonist, and oxotremorine, which is a close analogue of Oxo-M. Both compounds inhibited KCNQ2/3 currents via activation of M1 muscarinic acetylcholine receptors but, in contrast to Oxo-M, they did not directly inhibit KCNQ2/3 channels. Xanomeline and oxotremorine do not contain a positively charged trimethylammonium moiety that is present in Oxo-M, suggesting that such a charged moiety could be a crucial component mediating this newly described direct inhibition of KCNQ2/3 channels.
authors: Eli Lilly and Company, Lilly Research Centre, Erl Wood Manor, Sunninghill Road, Windlesham GU20 6PH, United Kingdom. Electronic address: zwart_ruud@lilly.com.
authors: Ruud
authors: R
authors: Zwart
authors: Eli Lilly and Company, Lilly Research Centre, Erl Wood Manor, Sunninghill Road, Windlesham GU20 6PH, United Kingdom.
authors: Hannah
authors: H
authors: Reed
authors: Eli Lilly and Company, Lilly Research Centre, Erl Wood Manor, Sunninghill Road, Windlesham GU20 6PH, United Kingdom.
authors: Sophie
authors: S
authors: Clarke
authors: Eli Lilly and Company, Lilly Research Centre, Erl Wood Manor, Sunninghill Road, Windlesham GU20 6PH, United Kingdom.
authors: Emanuele
authors: E
authors: Sher
mesh_terms: D000818:Animals; D006801:Humans; D051658:KCNQ2 Potassium Channel / Q000037:antagonists & inhibitors*; D051659:KCNQ3 Potassium Channel / Q000037:antagonists & inhibitors*; D010095:Oxotremorine / Q000031:analogs & derivatives* / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D011725:Pyridines / Q000494:pharmacology; D043643:Receptor, Muscarinic M1 / Q000378:metabolism; D013830:Thiadiazoles / Q000494:pharmacology; D014981:Xenopus
chemical_list: D051658:KCNQ2 Potassium Channel; D051659:KCNQ3 Potassium Channel; D026902:Potassium Channel Blockers; D011725:Pyridines; D043643:Receptor, Muscarinic M1; D013830:Thiadiazoles; D010095:Oxotremorine; C042743:oxotremorine M; C075257:xanomeline
keywords: KCNQ2/3 channels; M-current; M1 muscarinic acetylcholine receptors; Oxotremorine-M; Recombinant; Xenopus oocytes