Muscarinic receptor-mediated excitation of rat intracardiac ganglion neurons.
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 Ca(2+) markedly increased the OxoM-induced current (IOxoM). The inward IOxoM in the absence of extracellular Ca(2+) 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 Ca(2+)/calmodulin-dependent protein kinase II, had no effect. These results suggest that the activation mechanism involves a PLC pathway, release of Ca(2+) from intracellular Ca(2+) stores and calmodulin. The cation channels activated by muscarinic receptors may play an important role in neuronal membrane depolarization in rat intracardiac ganglion neurons.
Department of Physiology, School of Allied Health Sciences, Kitasato University, Sagamihara 252-0373, Japan; Department of Anesthesiology, Wakayama Medical University, Wakayama 641-0012, Japan.
Michiko
M
Hirayama
Department of Physiology, School of Allied Health Sciences, Kitasato University, Sagamihara 252-0373, Japan.
Masanori
M
Ogata
Department of Anesthesiology, Wakayama Medical University, Wakayama 641-0012, Japan.
Tomoyuki
T
Kawamata
Department of Physiology, School of Allied Health Sciences, Kitasato University, Sagamihara 252-0373, Japan. Electronic address: isibasih@kitasato-u.ac.jp.
Hitoshi
H
Ishibashi
D000818:Animals; D002118:Calcium / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D002478:Cells, Cultured; D005726:Ganglia, Parasympathetic / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018721:Muscarinic Agonists / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010095:Oxotremorine / Q000031:analogs & derivatives / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D017208:Rats, Wistar; D043643:Receptor, Muscarinic M1 / Q000819:agonists / Q000378:metabolism*; D043587:Receptor, Muscarinic M3 / Q000819:agonists / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism
D002147:Calmodulin; D018721:Muscarinic Agonists; D043643:Receptor, Muscarinic M1; D043587:Receptor, Muscarinic M3; D010095:Oxotremorine; C042743:oxotremorine M; D012964:Sodium; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D010738:Type C Phospholipases; D002118:Calcium
Action potential firing; Muscarinic receptors; Nonselective cationic channels; Parasympathetic ganglion; Perforated patch-clamp recording