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Tompkins JD, Hoover DB, Havton LA, Patel JC, Cho Y, Smith EH, Biscola NP, Ajijola OA, Shivkumar K, Ardell JL. Comparative specialization of intrinsic cardiac neurons in humans, mice, and pigs. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.04.588174. [PMID: 38645175 PMCID: PMC11030249 DOI: 10.1101/2024.04.04.588174] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/23/2024]
Abstract
Intrinsic cardiac neurons (ICNs) play a crucial role in the proper functioning of the heart; yet a paucity of data pertaining to human ICNs exists. We took a multidisciplinary approach to complete a detailed cellular comparison of the structure and function of ICNs from mice, pigs, and humans. Immunohistochemistry of whole and sectioned ganglia, transmission electron microscopy, intracellular microelectrode recording and dye filling for quantitative morphometry were used to define the neurophysiology, histochemistry, and ultrastructure of these cells across species. The densely packed, smaller ICNs of mouse lacked dendrites, formed axosomatic connections, and had high synaptic efficacy constituting an obligatory synapse. At Pig ICNs, a convergence of subthreshold cholinergic inputs onto extensive dendritic arbors supported greater summation and integration of synaptic input. Human ICNs were tonically firing, with synaptic stimulation evoking large suprathreshold excitatory postsynaptic potentials like mouse, and subthreshold potentials like pig. Ultrastructural examination of synaptic terminals revealed conserved architecture, yet small clear vesicles (SCVs) were larger in pigs and humans. The presence and localization of ganglionic neuropeptides was distinct, with abundant VIP observed in human but not pig or mouse ganglia, and little SP or CGRP in pig ganglia. Action potential waveforms were similar, but human ICNs had larger after-hyperpolarizations. Intrinsic excitability differed; 93% of human cells were tonic, all pig neurons were phasic, and both phasic and tonic phenotypes were observed in mouse. In combination, this publicly accessible, multimodal atlas of ICNs from mice, pigs, and humans identifies similarities and differences in the evolution of ICNs.
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Affiliation(s)
- John D. Tompkins
- UCLA Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
| | - Donald B. Hoover
- Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, TN, USA
| | - Leif A. Havton
- Departments of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- Department of Neurology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Janaki C. Patel
- UCLA Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
| | - Youngjin Cho
- UCLA Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
| | - Elizabeth H. Smith
- Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, TN, USA
| | - Natalia P. Biscola
- Department of Neurology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Olujimi A. Ajijola
- UCLA Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
| | - Kalyanam Shivkumar
- UCLA Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
| | - Jeffrey L. Ardell
- UCLA Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
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Harper AA, Adams DJ. Electrical properties and synaptic transmission in mouse intracardiac ganglion neurons in situ. Physiol Rep 2021; 9:e15056. [PMID: 34582125 PMCID: PMC8477906 DOI: 10.14814/phy2.15056] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Revised: 08/25/2021] [Accepted: 09/08/2021] [Indexed: 12/19/2022] Open
Abstract
The intrinsic cardiac nervous system represents the final site of signal integration for neurotransmission to the myocardium to enable local control of cardiac performance. The electrophysiological characteristics and ganglionic transmission of adult mouse intrinsic cardiac ganglion (ICG) neurons were investigated using a whole-mount ganglion preparation of the excised right atrial ganglion plexus and intracellular microelectrode recording techniques. The passive and active electrical properties of ICG neurons and synaptic transmission including synaptic response strength and efficacy as a function of stimulation frequency were examined. The resting membrane potential and input resistance of ICG neurons were -47.9 ± 4.0 mV and 197.2 ± 81.5 MΩ, respectively. All neurons had somatic action potentials with overshoots of >+15 mV and after-hyperpolarizations having an average of 10 mV amplitude and ~45 ms half duration. Phasic discharge activities were recorded from the majority of neurons studied and several types of excitatory synaptic responses were recorded following inputs from the vagus or interganglionic nerve trunk(s). Most postganglionic neurons (>75%) received a strong, suprathreshold synaptic input and reliably followed high-frequency repetitive nerve stimulation up to at least 50 Hz. Nerve-evoked synaptic transmission was blocked by extracellular Cd2+ , ω-conotoxin CVIE, or α-conotoxin RegIIA, a selective α3-containing nicotinic acetylcholine receptor antagonist. Synaptic transmission and the electrical properties of murine ICG neurons contribute to the pattern of discharge which regulates chronotropic, dromotropic, and inotropic elements of cardiac function.
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Affiliation(s)
- Alexander A. Harper
- Illawarra Health and Medical Research Institute (IHMRI)University of WollongongWollongongNew South WalesAustralia
| | - David J. Adams
- Illawarra Health and Medical Research Institute (IHMRI)University of WollongongWollongongNew South WalesAustralia
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3
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Hanna P, Dacey MJ, Brennan J, Moss A, Robbins S, Achanta S, Biscola NP, Swid MA, Rajendran PS, Mori S, Hadaya JE, Smith EH, Peirce SG, Chen J, Havton LA, Cheng Z(J, Vadigepalli R, Schwaber J, Lux RL, Efimov I, Tompkins JD, Hoover DB, Ardell JL, Shivkumar K. Innervation and Neuronal Control of the Mammalian Sinoatrial Node a Comprehensive Atlas. Circ Res 2021; 128:1279-1296. [PMID: 33629877 PMCID: PMC8284939 DOI: 10.1161/circresaha.120.318458] [Citation(s) in RCA: 55] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
[Figure: see text].
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Affiliation(s)
- Peter Hanna
- University of California Los Angeles (UCLA) Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, Department of Medicine
- UCLA Molecular, Cellular & Integrative Physiology Program, UCLA
| | - Michael J. Dacey
- University of California Los Angeles (UCLA) Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, Department of Medicine
- UCLA Molecular, Cellular & Integrative Physiology Program, UCLA
| | - Jaclyn Brennan
- Bioengineering, George Washington University, Washington, DC
| | - Alison Moss
- Daniel Baugh Institute for Functional Genomics/Computational Biology, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, PA
| | - Shaina Robbins
- Daniel Baugh Institute for Functional Genomics/Computational Biology, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, PA
| | - Sirisha Achanta
- Daniel Baugh Institute for Functional Genomics/Computational Biology, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, PA
| | | | - Mohammed A. Swid
- University of California Los Angeles (UCLA) Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, Department of Medicine
| | - Pradeep S. Rajendran
- University of California Los Angeles (UCLA) Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, Department of Medicine
| | - Shumpei Mori
- University of California Los Angeles (UCLA) Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, Department of Medicine
| | - Joseph E. Hadaya
- University of California Los Angeles (UCLA) Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, Department of Medicine
| | | | | | - Jin Chen
- University of Central Florida, Burnett School of Biomedical Sciences, College of Medicine, Orlando, FL
| | - Leif A. Havton
- Neurology, Icahn School of Medicine at Mount Sinai, New York City, NY
- Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY
- VA RR&D National Center of Excellence for the Medical Consequences of Spinal and; Cord Injury and Neurology Service, James J. Peters Veterans Administration Medical Center, Bronx, NY
| | - Zixi (Jack) Cheng
- University of Central Florida, Burnett School of Biomedical Sciences, College of Medicine, Orlando, FL
| | - Rajanikanth Vadigepalli
- Daniel Baugh Institute for Functional Genomics/Computational Biology, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, PA
| | - James Schwaber
- Daniel Baugh Institute for Functional Genomics/Computational Biology, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, PA
| | - Robert L. Lux
- University of California Los Angeles (UCLA) Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, Department of Medicine
| | - Igor Efimov
- Bioengineering, George Washington University, Washington, DC
| | - John D. Tompkins
- University of California Los Angeles (UCLA) Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, Department of Medicine
| | - Donald B. Hoover
- Biomedical Sciences
- Center of Excellence in Inflammation, Infectious Disease and Immunity, James H. Quillen College of Medicine, East Tennessee State University
| | - Jeffrey L. Ardell
- University of California Los Angeles (UCLA) Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, Department of Medicine
- UCLA Molecular, Cellular & Integrative Physiology Program, UCLA
| | - Kalyanam Shivkumar
- University of California Los Angeles (UCLA) Cardiac Arrhythmia Center and Neurocardiology Research Program of Excellence, Department of Medicine
- UCLA Molecular, Cellular & Integrative Physiology Program, UCLA
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4
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Ashton JL, Argent L, Smith JEG, Jin S, Sands GB, Smaill BH, Montgomery JM. Evidence of structural and functional plasticity occurring within the intracardiac nervous system of spontaneously hypertensive rats. Am J Physiol Heart Circ Physiol 2020; 318:H1387-H1400. [DOI: 10.1152/ajpheart.00020.2020] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We have developed intracardiac neuron whole cell recording techniques in atrial preparations from control and spontaneous hypertensive rats. This has enabled the identification of significant synaptic plasticity in the intracardiac nervous system, including enhanced postsynaptic current frequency, increased synaptic terminal density, and altered postsynaptic receptors. This increased synaptic drive together with altered cardiac neuron electrophysiology could increase intracardiac nervous system excitability and contribute to the substrate for atrial arrhythmia in hypertensive heart disease.
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Affiliation(s)
- Jesse L. Ashton
- Department of Physiology, Manaaki Mānawa Centre for Heart Research, University of Auckland, Auckland, New Zealand
| | - Liam Argent
- Department of Physiology, Manaaki Mānawa Centre for Heart Research, University of Auckland, Auckland, New Zealand
| | - Joscelin E. G. Smith
- Department of Physiology, Manaaki Mānawa Centre for Heart Research, University of Auckland, Auckland, New Zealand
| | - Sangjun Jin
- Department of Physiology, Manaaki Mānawa Centre for Heart Research, University of Auckland, Auckland, New Zealand
| | - Gregory B. Sands
- Department of Physiology, Manaaki Mānawa Centre for Heart Research, University of Auckland, Auckland, New Zealand
- Bioengineering Institute, Manaaki Mānawa Centre for Heart Research, University of Auckland, Auckland, New Zealand
| | - Bruce H. Smaill
- Department of Physiology, Manaaki Mānawa Centre for Heart Research, University of Auckland, Auckland, New Zealand
- Bioengineering Institute, Manaaki Mānawa Centre for Heart Research, University of Auckland, Auckland, New Zealand
| | - Johanna M. Montgomery
- Department of Physiology, Manaaki Mānawa Centre for Heart Research, University of Auckland, Auckland, New Zealand
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5
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Smith FM, Vermeulen M, Cardinal R. Long-term spinal cord stimulation modifies canine intrinsic cardiac neuronal properties and ganglionic transmission during high-frequency repetitive activation. Physiol Rep 2016; 4:4/13/e12855. [PMID: 27401459 PMCID: PMC4945838 DOI: 10.14814/phy2.12855] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Accepted: 06/16/2016] [Indexed: 12/28/2022] Open
Abstract
Long‐term spinal cord stimulation (SCS) applied to cranial thoracic SC segments exerts antiarrhythmic and cardioprotective actions in the canine heart in situ. We hypothesized that remodeling of intrinsic cardiac neuronal and synaptic properties occur in canines subjected to long‐term SCS, specifically that synaptic efficacy may be preferentially facilitated at high presynaptic nerve stimulation frequencies. Animals subjected to continuous SCS for 5–8 weeks (long‐term SCS: n = 17) or for 1 h (acute SCS: n = 4) were compared with corresponding control animals (long‐term: n = 15, acute: n = 4). At termination, animals were anesthetized, the heart was excised and neurones from the right atrial ganglionated plexus were identified and studied in vitro using standard intracellular microelectrode technique. Main findings were as follows: (1) a significant reduction in whole cell membrane input resistance and acceleration of the course of AHP decay identified among phasic neurones from long‐term SCS compared with controls, (2) significantly more robust synaptic transmission to rundown in long‐term SCS during high‐frequency (10–40 Hz) presynaptic nerve stimulation while recording from either phasic or accommodating postsynaptic neurones; this was associated with significantly greater posttrain excitatory postsynaptic potential (EPSP) numbers in long‐term SCS than control, and (3) synaptic efficacy was significantly decreased by atropine in both groups. Such changes did not occur in acute SCS. In conclusion, modification of intrinsic cardiac neuronal properties and facilitation of synaptic transmission at high stimulation frequency in long‐term SCS could improve physiologically modulated vagal inputs to the heart.
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Affiliation(s)
- Frank M Smith
- Department of Medical Neuroscience, Faculty of Medicine Dalhousie University, Halifax, Nova Scotia, Canada
| | - Michel Vermeulen
- Department of Pharmacology, Faculté de médecine Université de Montréal and Centre de recherche Hôpital du Sacré-Cœur de Montréal, Montréal, Quebec, Canada
| | - René Cardinal
- Department of Pharmacology, Faculté de médecine Université de Montréal and Centre de recherche Hôpital du Sacré-Cœur de Montréal, Montréal, Quebec, Canada
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6
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Abstract
Cardiac control is mediated via a series of reflex control networks involving somata in the (i) intrinsic cardiac ganglia (heart), (ii) intrathoracic extracardiac ganglia (stellate, middle cervical), (iii) superior cervical ganglia, (iv) spinal cord, (v) brainstem, and (vi) higher centers. Each of these processing centers contains afferent, efferent, and local circuit neurons, which interact locally and in an interdependent fashion with the other levels to coordinate regional cardiac electrical and mechanical indices on a beat-to-beat basis. This control system is optimized to respond to normal physiological stressors (standing, exercise, and temperature); however, it can be catastrophically disrupted by pathological events such as myocardial ischemia. In fact, it is now recognized that autonomic dysregulation is central to the evolution of heart failure and arrhythmias. Autonomic regulation therapy is an emerging modality in the management of acute and chronic cardiac pathologies. Neuromodulation-based approaches that target select nexus points of this hierarchy for cardiac control offer unique opportunities to positively affect therapeutic outcomes via improved efficacy of cardiovascular reflex control. As such, understanding the anatomical and physiological basis for such control is necessary to implement effectively novel neuromodulation therapies. © 2016 American Physiological Society. Compr Physiol 6:1635-1653, 2016.
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Affiliation(s)
- Jeffrey L Ardell
- Los Angeles (UCLA) Cardiac Arrhythmia Center, David Geffen School of Medicine, University of California, Los Angeles, California, USA.,UCLA Neurocardiology Research Center of Excellence, David Geffen School of Medicine, Los Angeles, California, USA
| | - John Andrew Armour
- Los Angeles (UCLA) Cardiac Arrhythmia Center, David Geffen School of Medicine, University of California, Los Angeles, California, USA.,UCLA Neurocardiology Research Center of Excellence, David Geffen School of Medicine, Los Angeles, California, USA
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7
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Muscarinic receptor-mediated excitation of rat intracardiac ganglion neurons. Neuropharmacology 2015; 95:395-404. [DOI: 10.1016/j.neuropharm.2015.04.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2014] [Revised: 03/13/2015] [Accepted: 04/14/2015] [Indexed: 11/23/2022]
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8
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Mitchelson FJ. The pharmacology of McN-A-343. Pharmacol Ther 2012; 135:216-45. [DOI: 10.1016/j.pharmthera.2012.05.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Accepted: 05/07/2012] [Indexed: 01/01/2023]
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Abramochkin DV, Nurullin LF, Borodinova AA, Tarasova NV, Sukhova GS, Nikolsky EE, Rosenshtraukh LV. Non-quantal release of acetylcholine from parasympathetic nerve terminals in the right atrium of rats. Exp Physiol 2009; 95:265-73. [PMID: 19767403 DOI: 10.1113/expphysiol.2009.050302] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Acetylcholinesterase (AChE) inhibitors provoke typical cholinergic effects in the isolated right atrium of the rat due to the accumulation of acetylcholine (ACh). Our study was designed to show that in the absence of vagal impulse activity, ACh is released from the parasympathetic nerve fibres by means of non-quantal secretion. The conventional microelectrode technique was used to study changes in action potential (AP) configuration in the right atrium preparation of rats during application of AChE inhibitors. Staining with the lipophilic fluorescent dye FM1-43 was used to demonstrate the presence of endocytosis in cholinergic endings. The AChE inhibitors armin (10(7)-10(5)m) and neostigmine (10(7) to 5 x 10(6)m) caused a reduction of AP duration and prolonged the cycle length. These effects were abolished by atropine and were therefore mediated by ACh accumulated in the myocardium during AChE inhibition. Putative block of impulse activity of the postganglionic neurons by tetrodotoxin (5 x 10(7)m) and blockade of ganglionic transmission by hexomethonium (2 x 10(4)m), as well as blockade of all forms of quantal release with Clostridium botulinum type A toxin (50 U ml(1)), did not alter the effects of armin. Experiments with FM1-43 dye confirmed the effective block of exocytosis by botulinum toxin. Selective inhibition of the choline uptake system using hemicholinium III (10(5)m), which blocks non-quantal release at the neuromuscular junction, suppressed the effects of AChE inhibitors. Thus, accumulation of ACh is likely to be caused by non-quantal release from cholinergic terminals. We propose that non-quantal release of ACh, shown previously at the neuromuscular junction, is present in cholinergic postganglionic fibres of the rat heart in addition to quantal release.
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Affiliation(s)
- Denis V Abramochkin
- Department of Human and Animal Physiology, Biological Faculty of the Moscow State University, Leninskije Gory, 1, 12, Moscow, Russia.
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10
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Tompkins JD, Ardell JL, Hoover DB, Parsons RL. Neurally released pituitary adenylate cyclase-activating polypeptide enhances guinea pig intrinsic cardiac neurone excitability. J Physiol 2007; 582:87-93. [PMID: 17495034 PMCID: PMC2075297 DOI: 10.1113/jphysiol.2007.134965] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Intracellular recordings were made in vitro from guinea-pig cardiac ganglia to determine whether endogenous neuropeptides such as pituitary adenylate cyclase-activating polypeptide (PACAP) or substance P released during tetanic neural stimulation modulate cardiac neurone excitability and/or contribute to slow excitatory postsynaptic potentials (sEPSPs). When nicotinic and muscarinic receptors were blocked by hexamethonium and atropine, 20 Hz stimulation for 10 s initiated a sEPSP in all innervated neurones. In 40% of the cells, excitability was enhanced after termination of the sEPSP. This suggested that non-cholinergic receptor-mediated mechanisms contributed to the sEPSP and modulated neuronal excitability. Exogenous PACAP and substance P initiated a slow depolarization in the neurones whereas neuronal excitability was only increased by PACAP. When ganglia were treated with the PAC1 antagonist PACAP6-38 (500 nM), the sEPSP evoked by 20 Hz stimulation was reduced by approximately 50% and an enhanced excitability occurred in only 10% of the cells. These observations suggested that PACAP released from preganglionic nerve terminals during tetanic stimulation enhanced neuronal excitability and evoked sEPSPs. After addition of 1 nM PACAP to the bath, 7 of 9 neurones exhibited a tonic firing pattern whereas in untreated preparations, the neurons had a phasic firing pattern. PACAP6-38 (500 nM) diminished the increase in excitability caused by 1 nM PACAP so that only 4 of 13 neurones exhibited a tonic firing pattern and the other 9 cells retained a phasic firing pattern. These findings indicate that PACAP can be released by tetanic neural stimulation in vitro and increase the excitability of intrinsic cardiac neurones. We hypothesize that in vivo PACAP released during preganglionic firing may modulate neurotransmission within the intrinsic cardiac ganglia.
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MESH Headings
- Animals
- Atropine/pharmacology
- Autonomic Fibers, Preganglionic/metabolism
- Electric Stimulation/methods
- Excitatory Postsynaptic Potentials
- Ganglia, Parasympathetic/cytology
- Ganglia, Parasympathetic/drug effects
- Ganglia, Parasympathetic/metabolism
- Guinea Pigs
- Heart/innervation
- Heart Atria/innervation
- Hexamethonium/pharmacology
- In Vitro Techniques
- Kinetics
- Muscarinic Antagonists/pharmacology
- Neurons/drug effects
- Neurons/metabolism
- Nicotinic Antagonists/pharmacology
- Peptide Fragments/pharmacology
- Pituitary Adenylate Cyclase-Activating Polypeptide/metabolism
- Pituitary Adenylate Cyclase-Activating Polypeptide/pharmacology
- Receptors, Muscarinic/drug effects
- Receptors, Nicotinic/drug effects
- Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I/antagonists & inhibitors
- Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I/metabolism
- Substance P/pharmacology
- Synaptic Transmission/drug effects
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Affiliation(s)
- John D Tompkins
- Department of Anatomy and Neurobiology, College of Medicine, University of Vermont, Burlington, VT 05405, USA
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Rimmer K, Harper AA. Developmental Changes in Electrophysiological Properties and Synaptic Transmission in Rat Intracardiac Ganglion Neurons. J Neurophysiol 2006; 95:3543-52. [PMID: 16611840 DOI: 10.1152/jn.01220.2005] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We charted postnatal changes in the intrinsic electrophysiological properties and synaptic responses of rat intrinsic cardiac ganglion (ICG) neurons. We developed a whole-mount ganglion preparation of the excised right atrial ganglion plexus. Using intracellular recordings and nerve stimulation we tested the hypothesis that substantial transformations in the intrinsic electrical characteristics and synaptic transmission accompany postnatal development. Membrane potential ( Em) did not change but time constant (τ) and cell capacitance increased with postnatal development. Accordingly, input resistance ( Rin) decreased but specific membrane resistance ( Rm) increased postnatally. Comparison of the somatic active membrane properties revealed significant changes in electrical phenotype. All neonatal neurons had somatic action potentials (APs) with small overshoots and small afterhyperpolarizations (AHPs). Adult neurons had somatic APs with large overshoots and large AHP amplitudes. The range of AHP duration was larger in adults than in neonates. The AP characteristics of juvenile neurons resembled those of adults, with the exception of AHP duration, which fell midway between neonate and adult values. Phasic, multiply adapting, and tonic evoked discharge activities were recorded from ICG neurons. Most neurons displayed phasic discharge at each developmental stage. All neurons received excitatory synaptic inputs from the vagus or interganglionic nerve trunk(s), the strength of which did not change significantly with postnatal age. The changes in the electrophysiological properties of the postganglionic neuron suggest that increased complexity of parasympathetic regulation of cardiac function accompanies postnatal development.
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Affiliation(s)
- Katrina Rimmer
- Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
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12
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Beker F, Weber M, Fink RHA, Adams DJ. Muscarinic and nicotinic ACh receptor activation differentially mobilize Ca2+ in rat intracardiac ganglion neurons. J Neurophysiol 2003; 90:1956-64. [PMID: 12761283 DOI: 10.1152/jn.01079.2002] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The origin of intracellular Ca2+ concentration ([Ca2+]i) transients stimulated by nicotinic (nAChR) and muscarinic (mAChR) receptor activation was investigated in fura-2-loaded neonatal rat intracardiac neurons. ACh evoked [Ca2+]i increases that were reduced to approximately 60% of control in the presence of either atropine (1 microM) or mecamylamine (3 microM) and to <20% in the presence of both antagonists. Removal of external Ca2+ reduced ACh-induced responses to 58% of control, which was unchanged in the presence of mecamylamine but reduced to 5% of control by atropine. The nAChR-induced [Ca2+]i response was reduced to 50% by 10 microM ryanodine, whereas the mAChR-induced response was unaffected by ryanodine, suggesting that Ca2+ release from ryanodine-sensitive Ca2+ stores may only contribute to the nAChR-induced [Ca2+]i responses. Perforated-patch whole cell recording at -60 mV shows that the rise in [Ca2+]i is concomitant with slow outward currents on mAChR activation and with rapid inward currents after nAChR activation. In conclusion, different signaling pathways mediate the rise in [Ca2+]i and membrane currents evoked by ACh binding to nicotinic and muscarinic receptors in rat intracardiac neurons.
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Affiliation(s)
- Friederike Beker
- School of Biomedical Sciences, University of Queensland, Brisbane, Queeensland 4072, Australia
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Wang N, Orr-Urtreger A, Korczyn AD. The role of neuronal nicotinic acetylcholine receptor subunits in autonomic ganglia: lessons from knockout mice. Prog Neurobiol 2002; 68:341-60. [PMID: 12531234 DOI: 10.1016/s0301-0082(02)00106-5] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Neuronal nicotinic acetylcholine receptors (nAChR), composed of 12 subunits (alpha2-alpha10, beta2-beta4), are expressed in autonomic ganglia, playing a central role in autonomic transmission. The repertoire of nicotinic subunits in autonomic ganglia includes alpha3, alpha5, alpha7, beta2 and beta4 subunits. In the last 10 years, heterologous expression studies have revealed much about the nature of neuronal nAChRs. However, there is only limited understanding of subunit actions in autonomic system. Functional deletions of subunit by gene knockout in animals could overcome these limitations. We review recent studies on nAChRs on autonomic ganglia for physiological and pharmacological properties and potential locations of the subunits.
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Affiliation(s)
- Ningshan Wang
- Department of Physiology and Pharmacology, Sackler Medical School, Tel Aviv University, Ramat Aviv, Israel
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15
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Smith FM, McGuirt AS, Leger J, Armour JA, Ardell JL. Effects of chronic cardiac decentralization on functional properties of canine intracardiac neurons in vitro. Am J Physiol Regul Integr Comp Physiol 2001; 281:R1474-82. [PMID: 11641118 DOI: 10.1152/ajpregu.2001.281.5.r1474] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Although intrinsic cardiac neurons display ongoing activity after chronic interruption of extrinsic autonomic inputs to the heart, the effects of decentralization on individual neurons remain unknown. The objective of this study was to determine the effects of chronic (3-4 wk) surgical decentralization on intracellular properties of, and neurotransmission among, neurons contained within the canine intrinsic right atrial ganglionated plexus in vitro. Properties of neurons from decentralized hearts were compared with those of neurons from sham-operated hearts (controls). Two populations of neurons were identified by their firing behavior in response to intracellular current injection. Fifty-nine percent of control neurons and 72% of decentralized neurons were phasic (discharged one action potential on excitation). Forty-one percent of control neurons and 27% of decentralized neurons were accommodating (multiple discharge with decrementing frequency). After chronic decentralization, input resistance of phasic neurons increased, whereas the duration of afterhyperpolarization of accommodating neurons decreased. Postsynaptic responses to interganglionic nerve stimulation were evoked in 89% of control neurons and 83% of decentralized neurons; the majority of these responses involved nicotinic receptors. These results show that, after chronic decentralization, intrinsic cardiac neurons 1) undergo changes in membrane properties that may lead to increased excitability while 2) maintaining synaptic neurotransmission within the intrinsic cardiac ganglionated plexus.
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Affiliation(s)
- F M Smith
- Department of Anatomy and Neurobiology, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada.
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Smith FM, McGuirt AS, Hoover DB, Armour JA, Ardell JL. Chronic decentralization of the heart differentially remodels canine intrinsic cardiac neuron muscarinic receptors. Am J Physiol Heart Circ Physiol 2001; 281:H1919-30. [PMID: 11668052 DOI: 10.1152/ajpheart.2001.281.5.h1919] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The objective of the study was to determine if chronic interruption of all extrinsic nerve inputs to the heart alters cholinergic-mediated responses within the intrinsic cardiac nervous system (ICN). Extracardiac nerve inputs to the ICN were surgically interrupted (ICN decentralized). Three weeks later, the intrinsic cardiac right atrial ganglionated plexus (RAGP) was removed and intrinsic cardiac neuronal responses were evaluated electrophysiologically. Cholinergic receptor abundance was evaluated using autoradiography. In sham controls and chronic decentralized ICN ganglia, neuronal postsynaptic responses were mediated by acetylcholine, acting at nicotinic and muscarinic receptors. Muscarine- but not nicotine-mediated synaptic responses that were enhanced after chronic ICN decentralization. After chronic decentralization, muscarine facilitation of orthodromic neuronal activation increased. Receptor autoradiography demonstrated that nicotinic and muscarinic receptor density associated with the RAGP was unaffected by decentralization and that muscarinic receptors were tenfold more abundant than nicotinic receptors in the right atrial ganglia in each group. After chronic decentralization of the ICN, intrinsic cardiac neurons remain viable and responsive to cholinergic synaptic inputs. Enhanced muscarinic responsiveness of intrinsic cardiac neurons occurs without changes in receptor abundance.
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Affiliation(s)
- F M Smith
- Department of Anatomy and Neurobiology, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada
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Jeong SW, Ikeda SR, Wurster RD. Activation of various G-protein coupled receptors modulates Ca2+ channel currents via PTX-sensitive and voltage-dependent pathways in rat intracardiac neurons. JOURNAL OF THE AUTONOMIC NERVOUS SYSTEM 1999; 76:68-74. [PMID: 10323308 DOI: 10.1016/s0165-1838(99)00010-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
In the present study, we examined the ability of several putative neurotransmitters and neuromodulators to modulate voltage-dependent Ca2+ channel currents in adult rat intracardiac neurons. Of 17 compounds tested, acetylcholine (Ach), neuropeptide Y (NPY), norepinephrine (NE), and met-enkephalin (met-Enk) were effective modulators of the Ca2+ currents. The neurotransmitter-induced current inhibition was associated with slow activation kinetics and relief by a strong depolarizing prepulse. Overnight pretreatment of neurons with pertussis toxin (PTX, 500 ng/ml) significantly attenuated the neurotransmitter-induced current inhibition. Heterologous expression of transducin, a known chelator of G-protein betagamma subunits, almost completely abolished the neurotransmitter-induced current inhibition. Taken together, our data suggest that four different neurotransmitters inhibit the Ca2+ channel currents in adult rat intracardiac neurons via a pathway that is voltage-dependent, membrane-delimited, and utilizes betagamma subunits released from PTX-sensitive G-proteins. The Ca2+ channel inhibition by non-cholinergic neurotransmitters may play important roles in regulation of neuronal excitability and Ach release at synapses in intracardiac ganglia, thereby contributing to cholinergic control of cardiac functions.
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Affiliation(s)
- S W Jeong
- Laboratory of Molecular Physiology, Guthrie Research Institute, Sayre, PA 18840, USA.
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Cuevas J, Harper AA, Trequattrini C, Adams DJ. Passive and active membrane properties of isolated rat intracardiac neurons: regulation by H- and M-currents. J Neurophysiol 1997; 78:1890-902. [PMID: 9325358 DOI: 10.1152/jn.1997.78.4.1890] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The electrical characteristics of isolated neonatal rat intracardiac neurons were examined at 22 and 37 degrees C using the perforated-patch whole cell recording technique. The mean resting membrane potential was -52.0 mV at 37 degrees C and exhibited no temperature dependence. Lowering the temperature from 37 to 22 degrees C decreased the mean input resistance from 854 to 345 Momega, respectively, and reduced the membrane time constant approximately threefold yielding a Q10 of 2.1. Hyperpolarizing current pulses induced time-dependent rectification of the voltage response in all neurons at both temperatures. This behavior was previously not observed in dialyzed neurons and was reversibly blocked by external Cs+ (2 mM) but not Ba2+ (1 mM). Voltage-clamp studies of isolated neurons revealed a hyperpolarization-activated inward current. This inwardly rectifying conductance was isolated from other membrane currents using external Cs+. The time and voltage dependence of this current is consistent with Ih and contributes to the passive electrical properties of rat intracardiac neurons. In >90% of the neurons studied, depolarizing currents evoked firing of multiple, adapting, action potentials at 22 degrees C. The number of action potentials increased with current strength producing a mean discharge of 5.1 (+100 pA, 1 s pulse), which was attenuated at 37 degrees C to a mean of 1.4. The amplitude and kinetics of the slow, muscarine-sensitive inward and outward currents (IM) were highly temperature dependent. Lowering the temperature from 37 to 22 degrees C reduced the steady-state current amplitude by approximately one-third and the rate of deactivation of IM by six- to ninefold at all voltages examined. The average Q10 for the time constant of deactivation of IM was 3.7 +/- 0.3 (mean +/- SE). Acetylcholine (ACh) induced tonic discharges in response to depolarizing currents (+100 pA, 1 s pulse) at both temperatures. This effect of ACh was inhibited by the muscarinic receptor antagonists, pirenzepine (100 nM), and mL-toxin (60 nM). At 37 degrees C, a mean discharge of 1.5 was increased to 23.5 in the presence of ACh. A similar switch from phasic to tonic discharge was also produced by the potassium channel inhibitors, Ba2+ (1 mM) and uridine-5'-triphosphate (UTP; 100 microM), whereas cadmium, 4-aminopyridine, apamin, charybdotoxin, and dendrotoxin did not alter discharge activity. The pharmacological sensitivity profile and temperature dependence of the active membrane properties are consistent with the muscarine-sensitive potassium current (IM) regulating the discharge activity in rat intracardiac neurons.
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Affiliation(s)
- J Cuevas
- Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, Miami, Florida 33101, USA
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Jeong SW, Wurster RD. Muscarinic receptor activation modulates Ca2+ channels in rat intracardiac neurons via a PTX- and voltage-sensitive pathway. J Neurophysiol 1997; 78:1476-90. [PMID: 9310437 DOI: 10.1152/jn.1997.78.3.1476] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
With use of the whole cell patch-clamp technique, effects of the potent muscarinic agonist oxotremorine methiodide (oxo-M) on voltage-activated Ca2+ channel currents were investigated in acutely dissociated adult rat intracardiac neurons. In all tested neurons oxo-M reversibly inhibited the peak Ba2+ current. Inhibition of the peak Ba2+ current by oxo-M was associated with slowing of activation kinetics and was concentration dependent. The concentration of oxo-M necessary to produce a half-maximal inhibition of current and the maximal inhibition were 40.8 nM and 75.9%, respectively. Inhibitory effect of oxo-M was completely abolished by atropine. Among different muscarinic receptor antagonists, methoctramine (100 and 300 nM) significantly antagonized the current inhibition by oxo-M, with a negative logarithm of dissociation constant of 8.3 in adult rat intracardiac neurons. Internal dialysis of neurons with guanosine 5'-(thio)triphosphate (GTPgammaS, 0.5 mM) could mimic the muscarinic inhibition of the peak Ba2+ current and significantly occlude inhibitory effects of oxo-M. In addition, the internal dialysis of guanosine-5'-O-(2-thiodiphosphate) (GDPbetaS, 2 mM) also significantly reduced the muscarinic inhibition of the peak Ba2+ current by oxo-M. Inhibitory effects of oxo-M were significantly abolished by pertussis toxin (PTX, 200 and 400 ng/ml) but not by cholera toxin (400 ng/ml). Furthermore, the bath application of N-ethylmaleimide (50 microM) significantly reduced the inhibition of the peak Ba2+ current by oxo-M. The oxo-M shifted the activation curve derived from measurments of tail currents toward more positive potentials. A strong conditioning prepulse to +100 mV significantly relieved the muscarinic inhibition of peak Ba2+ currents by oxo-M and the GTPgammaS-induced current inhibition. In a series of experiments, changes in intracellular concentration of bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid and protein kinase activities failed to mimic or occlude the current inhibition by oxo-M. The dihydropyridine antagonist nifedipine (10 microM) was not able to occlude any of the inhibitory effects of oxo-M, and oxo-M (3 microM) failed to reduce the slow tail currents induced by the L-type agonist methyl 2,5-dimethyl-4-[2-(phenylmethyl)benzoyl]-1H-pyrrole-3-carboxylate (FPL 64176; 2 microM). However, omega-conotoxin (omega-CgTX) GVIA (1 microM) significantly occluded the muscarinic inhibition of the Ba2+ currents. In the presence of omega-CgTX GVIA (1 microM) and nifedipine (10 microM), oxo-M could further inhibit approximately 20% of the total Ca2+ current. After complete removal of N-, Q-, and L-type currents with use of omega-CgTX GVIA, omega-agatoxin IVA, and nifedipine, 70% of the R-type current (approximately 6-7% of the total current) was inhibited by oxo-M (3 microM). In conclusion, the M2 muscarinic receptor activation selectively inhibits N-, Q-, and R-type Ca2+ channel currents, sparing L-type Ca2+ channel currents mainly via a PTX- and voltage-sensitive pathway in adult rat intracardiac neurons.
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Affiliation(s)
- S W Jeong
- Department of Physiology, Loyola Stritch School of Medicine, Maywood, Illinois 60153, USA
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Jeong SW, Wurster RD. Calcium channel currents in acutely dissociated intracardiac neurons from adult rats. J Neurophysiol 1997; 77:1769-78. [PMID: 9114235 DOI: 10.1152/jn.1997.77.4.1769] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
With the use of the whole cell patch-clamp technique, multiple subtypes of voltage-activated calcium channels, as indicated by measuring Ba2+ currents, were pharmacologically identified in acutely dissociated intracardiac neurons from adult rats. All tested neurons that were held at -80 mV displayed only high-voltage-activated (HVA) Ca2+ channel currents that were completely blocked by 100 microM CdCl2. The current density of HVA Ca2+ currents was dependent on the external Ca2+ concentration. The Ba2+ (5 mM) currents were half-activated at -16.3 mV with a slope of 5.6 mV per e-fold change. The steady-state inactivation was also voltage dependent with half-inactivation at -33.7 mV and a slope of -12.1 mV per e-fold change. The most effective L-type channel activator, FPL 64176 (2 microM), enhanced the Ba2+ current in a voltage-dependent manner. When cells were held at -80 mV, the saturating concentration (10 microM) of nifedipine blocked approximately 11% of the control Ba2+ current. The major component of the Ca2+ channels was N type (63%), which was blocked by a saturating concentration (1 microM) of omega-conotoxin GVIA. Approximately 19% of the control Ba2+ current was sensitive to omega-conotoxin MVIIC (5 microM) but insensitive to low concentrations (30 and 100 nM) of omega-agatoxin IVA (omega-Aga IVA). In addition, a high concentration (1 microM) of omega-Aga IVA occluded the effect of omega-conotoxin MVIIC. Taken together, these results indicate that the omega-conotoxin MVIIC-sensitive current represents only the Q type of Ca2+ channels. The current that was insensitive to nifedipine and various toxins represents the R-type current (7%), which was sensitive to 100 microM NiCl2. In conclusion, the intracardiac neurons from adult rats express at least four different subtypes (L, N, Q, and R) of HVA Ca2+ channels. This information is essential for understanding the regulation of synaptic transmission and excitability of intracardiac neurons by different neurotransmitters and neural regulation of cardiac functions.
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Affiliation(s)
- S W Jeong
- Department of Physiology, Loyola Stritch School of Medicine, Maywood, Illinois 60153, USA
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Jones JF, Wang Y, Jordan D. Heart rate responses to selective stimulation of cardiac vagal C fibres in anaesthetized cats, rats and rabbits. J Physiol 1995; 489 ( Pt 1):203-14. [PMID: 8583404 PMCID: PMC1156804 DOI: 10.1113/jphysiol.1995.sp021042] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
1. The contribution of cardiac vagal C fibres to vagal chronotropic control in anaesthetized cats, rats and rabbits was analysed using electrical stimulation of the vagus nerve with a selective anodal block technique. 2. After bilateral vagotomy and pretreatment with atenolol, 10 Hz continuous selective stimulation of unmyelinated fibres in the cut peripheral end of the cervical vagus evoked a bradycardia in anaesthetized rats, cats and rabbits. With this stimulation protocol the three species exhibited a similar lengthening of the heart period (R-R interval) when expressed as a percentage of their basal cardiac interval. 3. The mechanism of action of the selective blocking technique was analysed by recording eighty-nine single A- (n = 12), B- (n = 22) and C-fibre (n = 55) vagal-projecting neurones in the medulla of the rat. This demonstrated that the technique can selectively block conduction in myelinated fibres and that 'break excitation' is seen mainly in unmyelinated fibres. Although thirty C fibres showed break excitation sixteen did not and this difference could not be correlated with their axonal conduction velocity, chronaxie or initial segment frequency following. 4. Using the anodal block technique the vagal effects on heart rate were reanalysed in the cat by incorporating a collision technique. B fibres were activated orthodromically to evoke cardioinhibition and simultaneously antidromically to collide with errant B-fibre spikes activated at the electrode producing anodal block. With this protocol it was noted that the B- and C-fibre bradycardias were not additive. Using a double anodal block and collision technique, it was demonstrated that this phenomenon was likely to be due to occlusion of the effects of B and C fibres. 5. In conclusion, in addition to the well-defined effects of vagal B fibres on heart rate, selective stimulation of vagal C fibres also had a cardioinhibitory effect in all three species studied. However, since the effects of cardiac C fibres on heart rate was small, these neurones alone cannot account for the cardioinhibition of the pulmonary chemoreflex. It is likely that activation of both B- and C-fibre cardiac vagal preganglionic neurones accounts for this reflex cardioinhibition.
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Affiliation(s)
- J F Jones
- Department of Physiology, Royal Free Hospital School of Medicine, London, UK
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Abstract
1. Properties of K+ currents were studied in isolated adult rat parasympathetic intracardiac neurones with the use of single-electrode voltage-clamp techniques. 2. A hyperpolarization-activated inward rectifier current was revealed when the membrane was clamped close to the resting level (-60 mV). The slowly developing inward relaxation had a mean amplitude of 450 pA at -150 mV, an activation threshold of -60 to -70 mV and a relaxation time constant of 41 ms at -120 mV. The current was reversibly blocked by Cs+ (1 mM) and became smaller with reduced [K+]o and [Na+]o, indicating that this inward rectifier current probably is a time- and voltage-dependent Na(+)-K+ current. 3. Step depolarizations from the holding potential of -80 mV evoked a transient (< 100 ms at -40 mV) outward K+ current (IA) which was blocked by 4-aminopyridine (4-AP, 1 mM). The time constants for IA inactivation were 20 ms at -50 mV and 16 ms at -20 mV. The steady-state activation and (removal of) inactivation curve showed a small overlap between -70 and -40 mV; the reversal potential of IA was close to EK. 4. Step hyperpolarizations from the depolarized potentials, i.e. -30 mV, revealed a slow inward relaxation associated with the deactivation of a time- and voltage-dependent current. The inward relaxation became faster at more hyperpolarized potentials and reversed at -85 and -53 mV in 4.7 and 15 mM [K+]o. This current was blocked by muscarine (20 microM) and Ba2+ (1 mM) but not affected by Cs+ (1 mM); this current may correspond to the M-current (IM). 5. Depolarization-activated outward K+ currents were evoked by holding the membrane close to the resting potential in the presence of tetrodotoxin (TTX, 3 microM), 4-AP (1 mM) and Ba2+ (1 mM). The amplitude of the outward relaxation and the tail current became smaller as the [K+]o was elevated. The outward tail current was reduced in a Ca(2+)-free solution and the residual current was eliminated by the addition of tetraethylammonium (TEA, 10 mM); the reversal potential was shifted in a direction predicted by the Nernst equation. These findings suggest the presence of delayed rectifier K+ current and Ca(2+)-activated K+ current. 6. Superfusion of TEA, Ba2+ and 4-AP, but not Cs+, induced rhythmic discharges in some of the otherwise quiescent intracardiac neurones.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- S X Xi-Moy
- Department of Anatomy and Neurobiology, Medical College of Ohio, Toledo 43614, USA
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Affiliation(s)
- T Akasu
- Department of Physiology, Kurume University School of Medicine, Japan
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Hoover DB, Baisden RH, Xi-Moy SX. Localization of muscarinic receptor mRNAs in rat heart and intrinsic cardiac ganglia by in situ hybridization. Circ Res 1994; 75:813-20. [PMID: 7923626 DOI: 10.1161/01.res.75.5.813] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Although the heart is considered a relatively pure source of m2 muscarinic receptors, the possible expression of other muscarinic receptor genes at discrete sites within the myocardium or by intrinsic cardiac ganglia had not been evaluated. Accordingly, the present study used in situ hybridization histochemistry with 35S-labeled oligonucleotide probes to address this issue. Initial experiments demonstrated that the localization of m2 mRNA was similar to that reported for muscarinic receptors labeled with the nonselective muscarinic antagonist quinuclidinyl benzilate; however, there were two important exceptions. The conducting system contained less message than expected, whereas the intrinsic cardiac ganglia contained more. The mismatch between muscarinic receptor and m2 mRNA densities in the conducting system could not be explained by the local expression of other muscarinic receptor genes, since m1, m3, and m4 mRNAs were not detected at this or any other site within the myocardium. However, the presence of a high density of prejunctional muscarinic receptors in the conducting system would be consistent with such a mismatch. Surprisingly, the intrinsic cardiac ganglia contained more than four times as much m2 mRNA as found in the atria. This level of message may be necessary for the production of prejunctional receptors on cholinergic nerve fibers within the heart and receptors localized to the ganglion cell bodies. The ganglia also contained smaller amounts of m1 and m4 mRNAs. These observations suggest that prejunctional muscarinic receptors could have a prominent role in regulating cholinergic neurotransmission in the conducting system and that multiple muscarinic receptors are present in the intrinsic cardiac ganglia.
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Affiliation(s)
- D B Hoover
- Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City 37614
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