The Journal of Neurophysiology Vol. 78 No. 4 October 1997, pp. 1903-1912
Copyright ©1997 The American Physiological Society

M₄ Muscarinic Receptor Activation Modulates Calcium Channel Currents in Rat Intracardiac Neurons

J. Cuevas and D. J. Adams

Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, Miami, Florida 33101; and Department of Physiology and Pharmacology, University of Queensland, Brisbane, Queensland 4072, Australia

Cuevas, J. and Adams, D. J. M₄ muscarinic receptor activation modulates calcium channel currents in rat intracardiac neurons. J. Neurophysiol. 78: 1903-1912, 1997. Modulation of high-voltage-activated Ca²⁺ channels by muscarinic receptor agonists was investigated in isolated parasympathetic neurons of neonatal rat intracardiac ganglia using the amphotericin B perforated-patch whole cell recording configuration of the patch-clamp technique. Focal application of the muscarinic agonists acetylcholine (ACh), muscarine, and oxotremorine-M to the voltage-clamped soma membrane reversibly depressed peak Ca²⁺ channel current amplitude. The dose-reponse relationship obtained for ACh-induced inhibition of Ba²⁺ current (I_Ba) exhibited a half-maximal inhibition at 6 nM. Maximal inhibition of I_Ba amplitude obtained with 100 µM ACh was ~75% compared with control at +10 mV. Muscarinic agonist-induced attenuation of Ca²⁺ channel currents was inhibited by the muscarinic receptor antagonists pirenzepine (300 nM) and m4-toxin (100 nM), but not by AF-DX 116 (300 nM) or m1-toxin (60 nM). The dose-response relationship obtained for antagonism of muscarine-induced inhibition of I_Ba by m4-toxin gave an IC₅₀ of 11 nM. These results suggest that muscarinic agonist-induced inhibition of high-voltage-activated Ca²⁺ channels in rat intracardiac neurons is mediated by the M₄ muscarinic receptor. M₄ receptor activation shifted the voltage dependence and depressed maximal activation of Ca²⁺ channels but had no effect on the steady-state inactivation of Ca²⁺ channels. Peak Ca²⁺ channel tail current amplitude was reduced 30% at +90 mV in the presence of ACh, indicating a voltage-independent component to the muscarinicreceptor-mediated inhibition. Both dihydropyridine- and -conotoxin GVIA-sensitive and -insensitive Ca²⁺ channels were inhibited by ACh, suggesting that the M₄ muscarinic receptor is coupled to multiple Ca²⁺ channel subtypes in these neurons. Inhibition of I_Ba amplitude by muscarinic agonists was also observed after cell dialysis using the conventional whole cell recording configuration. However, internal perfusion of the cell with 100 µM guanosine 5-O-(2-thiodiphosphate) trilithium salt (GDP--S) or incubation of the neurons in Pertussis toxin (PTX) abolished the modulation of I_Ba by muscarinic receptor agonists, suggesting the involvement of a PTX-sensitive G-protein in the signal transduction pathway. Given that ACh is the principal neurotransmitter mediating vagal innervation of the heart, the presence of this inhibitory mechanism in postganglionic intracardiac neurons suggests that it may serve for negative feedback regulation.

This article has been cited by other articles:

				Q. Yang, A. D. Sumner, H. L. Puhl, and V. Ruiz-Velasco M1 and M2 Muscarinic Acetylcholine Receptor Subtypes Mediate Ca2+ Channel Current Inhibition in Rat Sympathetic Stellate Ganglion Neurons J Neurophysiol, November 1, 2006; 96(5): 2479 - 2487. [Abstract] [Full Text] [PDF]

				H. Zhang and J. Cuevas {sigma} Receptor Activation Blocks Potassium Channels and Depresses Neuroexcitability in Rat Intracardiac Neurons J. Pharmacol. Exp. Ther., June 1, 2005; 313(3): 1387 - 1396. [Abstract] [Full Text] [PDF]

				T. Perez-Rosello, A. Figueroa, H. Salgado, C. Vilchis, F. Tecuapetla, J. N. Guzman, E. Galarraga, and J. Bargas Cholinergic Control of Firing Pattern and Neurotransmission in Rat Neostriatal Projection Neurons: Role of CaV2.1 and CaV2.2 Ca2+ Channels J Neurophysiol, May 1, 2005; 93(5): 2507 - 2519. [Abstract] [Full Text] [PDF]

				F. Beker, M. Weber, R. H. A. Fink, and D. J. Adams Muscarinic and Nicotinic ACh Receptor Activation Differentially Mobilize Ca2+ in Rat Intracardiac Ganglion Neurons J Neurophysiol, September 1, 2003; 90(3): 1956 - 1964. [Abstract] [Full Text] [PDF]

				J. Liu, M. S. Evans, and T. J.-F. Lee Presynaptic Muscarinic M2-Receptor-Mediated Inhibition of N-Type Ca2+ Channels in Cultured Sphenopalatine Ganglion: Direct Evidence for Acetylcholine Inhibition of Cerebral Nitrergic Neurogenic Vasodilation J. Pharmacol. Exp. Ther., July 1, 2002; 302(1): 397 - 405. [Abstract] [Full Text] [PDF]

				H. Zhang and J. Cuevas Sigma Receptors Inhibit High-Voltage-Activated Calcium Channels in Rat Sympathetic and Parasympathetic Neurons J Neurophysiol, June 1, 2002; 87(6): 2867 - 2879. [Abstract] [Full Text] [PDF]

				J. L. Krajewski, I. M. Dickerson, and L. T. Potter Site-Directed Mutagenesis of m1-Toxin1: Two Amino Acids Responsible for Stable Toxin Binding to M1 Muscarinic Receptors Mol. Pharmacol., October 1, 2001; 60(4): 725 - 731. [Abstract] [Full Text] [PDF]

				D. J. Adams and C. Trequattrini Opioid Receptor-Mediated Inhibition of omega -Conotoxin GVIA-Sensitive Calcium Channel Currents in Rat Intracardiac Neurons J Neurophysiol, February 1, 1998; 79(2): 753 - 762. [Abstract] [Full Text] [PDF]