Muscarinic receptor-mediated excitation of rat intracardiac ganglion neurons

• Published in: Neuropharmacology 2015-08, Vol.95, p.395-404
• Main Authors: Hirayama, Michiko, Ogata, Masanori, Kawamata, Tomoyuki, Ishibashi, Hitoshi
• Format: Article
• Language: English
• Subjects: Action potential firing; Animals; Calcium - metabolism; Calcium-Calmodulin-Dependent Protein Kinase Type 2 - antagonists & inhibitors; Calcium-Calmodulin-Dependent Protein Kinase Type 2 - metabolism; Calmodulin - metabolism; Cells, Cultured; Ganglia, Parasympathetic - drug effects; Ganglia, Parasympathetic - physiology; Membrane Potentials - drug effects; Membrane Potentials - physiology; Muscarinic Agonists - pharmacology; Muscarinic receptors; Neurons - drug effects; Neurons - physiology; Nonselective cationic channels; Oxotremorine - analogs & derivatives; Oxotremorine - pharmacology; Parasympathetic ganglion; Patch-Clamp Techniques; Perforated patch-clamp recording; Rats, Wistar; Receptor, Muscarinic M1 - agonists; Receptor, Muscarinic M1 - metabolism; Receptor, Muscarinic M3 - agonists; Receptor, Muscarinic M3 - metabolism; Sodium - metabolism; Type C Phospholipases - antagonists & inhibitors; Type C Phospholipases - metabolism
• ISSN: 0028-3908; 1873-7064
• DOI: 10.1016/j.neuropharm.2015.04.014

Modulation of the membrane excitability of rat parasympathetic intracardiac ganglion neurons by muscarinic receptors was studied using an amphotericin B-perforated patch-clamp recording configuration. Activation of muscarinic receptors by oxotremorine-M (OxoM) depolarized the membrane, accompanied by repetitive action potentials. OxoM evoked inward currents under voltage-clamp conditions at a holding potential of −60 mV. Removal of extracellular Ca2+ markedly increased the OxoM-induced current (IOxoM). The inward IOxoM in the absence of extracellular Ca2+ was fully inhibited by removal of extracellular Na+, indicating the involvement of non-selective cation channels. The IOxoM was inhibited by organic cation channel antagonists including SKF-96365 and ML-204. The IOxoM was antagonized by muscarinic receptor antagonists with the following potency: 4-DAMP > pirenzepine = darifenacin > methoctramine. Muscarinic toxin 7 (MT-7), a highly selective inhibitor for M1 receptor, produced partial inhibition of the IOxoM. In the presence of MT-7, concentration–inhibition curve of the M3-preferring antagonist darifenacin was shifted to the left. These results suggest the contribution of M1 and M3 receptors to the OxoM response. The IOxoM was inhibited by U-73122, a phospholipase C inhibitor. The membrane-permeable IP3 receptor blocker xestospongin C also inhibited the IOxoM. Furthermore, pretreatment with thapsigargin and BAPTA-AM inhibited the IOxoM, while KN-62, a blocker of Ca2+/calmodulin-dependent protein kinase II, had no effect. These results suggest that the activation mechanism involves a PLC pathway, release of Ca2+ from intracellular Ca2+ stores and calmodulin. The cation channels activated by muscarinic receptors may play an important role in neuronal membrane depolarization in rat intracardiac ganglion neurons. •Role of the muscarinic receptor in intracardiac ganglion neurons was investigated.•Muscarinic receptor agonist oxotremorine-M excited the ganglion neurons.•Oxotremorine-M induced cation currents via M1 and M3 receptors.•The oxotremorine-M response was mediated by intracellular Ca2+ release.•The results suggest that muscarinic receptors contribute to ganglionic transmission.