title: Excitation of rat sympathetic neurons via M1 muscarinic receptors independently of Kv7 channels.
abstract: The slow cholinergic transmission in autonomic ganglia is known to be mediated by an inhibition of Kv7 channels via M1 muscarinic acetylcholine receptors. However, in the present experiments using primary cultures of rat superior cervical ganglion neurons, the extent of depolarisation caused by the M1 receptor agonist oxotremorine M did not correlate with the extent of Kv7 channel inhibition in the very same neuron. This observation triggered a search for additional mechanisms. As the activation of M1 receptors leads to a boost in protein kinase C (PKC) activity in sympathetic neurons, various PKC enzymes were inhibited by different means. Interference with classical PKC isoforms led to reductions in depolarisations and in noradrenaline release elicited by oxotremorine M, but left the Kv7 channel inhibition by the muscarinic agonist unchanged. M1 receptor-induced depolarisations were also altered when extra- or intracellular Cl(-) concentrations were changed, as were depolarising responses to γ-aminobutyric acid. Depolarisations and noradrenaline release triggered by oxotremorine M were reduced by the non-selective Cl(-) channel blockers 4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulfonic acid and niflumic acid. Oxotremorine M induced slowly rising inward currents at negative membrane potentials that were blocked by inhibitors of Ca(2+)-activated Cl(-) and TMEM16A channels and attenuated by PKC inhibitors. These channel blockers also reduced oxotremorine M-evoked noradrenaline release. Together, these results reveal that slow cholinergic excitation of sympathetic neurons involves the activation of classical PKCs and of Ca(2+)-activated Cl(-) channels in addition to the well-known inhibition of Kv7 channels.
authors.affiliation: Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090, Vienna, Austria.
authors.forename: Isabella
authors.initials: I
authors.lastname: Salzer
authors.forename: Hend
authors.initials: H
authors.lastname: Gafar
authors.forename: Viola
authors.initials: V
authors.lastname: Gindl
authors.forename: Peter
authors.initials: P
authors.lastname: Mahlknecht
authors.forename: Helmut
authors.initials: H
authors.lastname: Drobny
authors.forename: Stefan
authors.initials: S
authors.lastname: Boehm
mesh_terms: D000200:Action Potentials; D000818:Animals; D002478:Cells, Cultured; D018118:Chloride Channels / Q000037:antagonists & inhibitors; D002712:Chlorides / Q000378:metabolism; D051656:KCNQ Potassium Channels / Q000378:metabolism*; D018721:Muscarinic Agonists / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism* / Q000502:physiology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D043643:Receptor, Muscarinic M1 / Q000819:agonists / Q000378:metabolism*; D017783:Superior Cervical Ganglion / Q000166:cytology / Q000378:metabolism* / Q000502:physiology
chemical_list: D018118:Chloride Channels; D002712:Chlorides; D051656:KCNQ Potassium Channels; D018721:Muscarinic Agonists; D043643:Receptor, Muscarinic M1; D011493:Protein Kinase C