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The Journal of Neuroscience, July 1, 2000, 20(13):5076-5082

Functional Nicotinic Acetylcholine Receptors That Mediate Ganglionic Transmission in Cardiac Parasympathetic Neurons

Steve Bibevski¹, Yuefang Zhou², J. Michael McIntosh³, Richard E. Zigmond², and Mark E. Dunlap^{1, 4}

Departments of ¹ Physiology and Biophysics and ² Neurosciences, Case Western Reserve University, Cleveland, Ohio 44106, ³ Departments of Biology and Psychiatry, University of Utah, Salt Lake City, Utah 84112, and ⁴ Department of Medicine-Cardiology, Veterans Affairs Medical Center, Cleveland, Ohio 44106

Nicotinic acetylcholine receptors (nAChRs) mediate ganglionic transmission in the peripheral autonomic nervous system in mammals. Functional neuronal nAChRs have been shown to assemble from a combination of  and  subunits, including 3, 5, 7, 2, and 4 in RNA-injected oocytes, but the subunit composition of functional neuronal nAChRs in vivo in mammals remains unknown. We examined the subunit composition of functional nAChRs in the intracardiac parasympathetic ganglion in a physiologically intact system in vivo. We report here that localized perfusion of the canine intracardiac ganglion in situ with an antagonist specific for nAChRs containing an 3/2 subunit interface (-conotoxin MII 100-200 nM) resulted in reversible attenuation of the sinus cycle length (SCL) response by ~70% to electrical stimulation of the preganglionic vagus nerve. Perfusion with antagonist specific for receptors containing an 3/4 subunit interface (-conotoxin AuIB 1 µM) resulted in attenuation in SCL responses (~20%) compared with baseline when applied by itself, but not in animals pretreated with -conotoxin MII. Perfusion of the ganglion with -bungarotoxin (1 µM, which blocks 7 receptors) caused a reduction in SCL response by ~30% compared with baseline when perfused on its own and when added after blockade with MII and AuIB. Perfusion with hexamethonium bromide resulted in complete blockade of ganglionic transmission, confirming total perfusion of the ganglion and the nicotinic nature of ganglionic transmission at this synapse. Immunohistochemistry using monoclonal antibodies against specific nicotinic subunits confirmed the presence of 3, 7, 2, and 4 subunits. We conclude that functional ganglionic transmission in the canine intracardiac ganglion is mediated primarily by receptors containing an 3/2 subunit interface, with a smaller contribution by receptors containing 7 nAChRs. Despite the presence of 4 subunits in functional channels, a contribution of a distinct 3/4 receptor population that does not include an 3/2 subunit interface was less clear.

Key words: nicotinic receptor; -conotoxin; neuronal; parasympathetic; cardiac; ganglion; acetylcholine

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Copyright © 2000 Society for Neuroscience  0270-6474/00/20135076-07$05.00/0

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