The transmission of physiological impulses across synaptic junctions relies fundamentally on specialized transmembrane proteins that transduce chemical messages into electrical and biochemical cascades. Among the most vital of these molecular transducers is the acetylcholine receptor (AChR), an integral membrane protein complex that binds the endogenous neurotransmitter acetylcholine to coordinate neuromuscular activity, autonomic regulation, and cognitive processing. Understanding the structural biology, electrophysiology, and pharmacology of acetylcholine receptors is central to modern neurobiology, clinical neurology, and psychiatric pharmacology.
Acetylcholine Receptor (AChR)
1. Concise Definition
An acetylcholine receptor (AChR) is an integral membrane protein that selectively binds the neurotransmitter acetylcholine (ACh), initiating downstream physiological responses in the target cell. Functioning as molecular transducers at chemical synapses and neuroeffector junctions, these receptors convert extracellular chemical stimuli into rapid electrical signals or sustained intracellular metabolic changes.
AChRs are categorized into two distinct pharmacological and structural classes: nicotinic acetylcholine receptors (nAChRs), which operate as ligand-gated ion channels mediating rapid excitatory neurotransmission, and muscarinic acetylcholine receptors (mAChRs), which belong to the superfamily of G protein-coupled receptors (GPCRs) regulating slower, modulatory cellular processes. Together, these receptor families maintain somatic motor control, autonomic tone throughout sympathetic and parasympathetic networks, and central nervous system functions including memory, attention, and sensory gating.
2. Etymology & Linguistic Origin
The term acetylcholine receptor combines chemical and biochemical nomenclature derived from classical linguistic roots. The prefix acetyl- originates from the Latin acetum, meaning “vinegar,” reflecting the presence of the acetic acid functional group (-COCH3). The word choline derives from the Ancient Greek cholē (χολή), signifying “bile,” because the chemical substance was first isolated from ox bile by German chemist Adolph Strecker in the mid-nineteenth century.
The noun receptor stems from the Latin receptor (“receiver” or “one who welcomes”), which itself traces back to the supine stem of recipere (“to receive back, to take in”), assembled from re- (“again” or “back”) and capere (“to take” or “to grasp”). German pharmacologist Paul Ehrlich popularized the concept of chemical “receptive substances” (Rezeptoren) at the turn of the twentieth century, laying the foundational vocabulary for molecular pharmacology and receptor theory.
3. Pronunciation & Grammatical Form
The term is pronounced phonetically in Standard English as /əˌsεt.əlˈkoʊ.liːn rɪˈsεp.tər/ (British English: /əˌsiː.taɪlˈkəʊ.liːn rɪˈsεp.tə/). It functions syntactically as a compound noun phrase, with the plural form represented as acetylcholine receptors. In scientific and clinical literature, the term is routinely abbreviated as AChR, or subdivided into nAChR (nicotinic acetylcholine receptor) and mAChR (muscarinic acetylcholine receptor).
When utilized as a modifier in biomedical discourse, the term frequently occurs in attributive constructions such as acetylcholine receptor subunit, AChR autoantibody titer, or AChR-mediated conductance. The phrase takes regular prepositional attachments, as seen in expressions like “agonist binding at the acetylcholine receptor” or “allosteric modulation of neuronal AChRs.”
4. Detailed Conceptual Explanation
The acetylcholine receptor system embodies one of the most comprehensively mapped communication channels in biological systems. At its core, an AChR acts as an energetic bridge spanning lipid bilayer membranes. In resting physiological states, these receptors exist in distinct conformations that maintain baseline cellular homeostasis. When action potentials reach presynaptic terminals, voltage-gated calcium channels trigger the exocytosis of acetylcholine into the synaptic cleft. Acetylcholine rapidly diffuses across the narrow extracellular space, engaging orthosteric recognition sites on the extracellular domains of post-junctional or extra-junctional AChRs.
The immediate structural response to ligand engagement diverges radically based on receptor classification. In nicotinic acetylcholine receptors, the binding of two acetylcholine molecules induces concerted tertiary and quaternary conformational rearrangements. The extracellular ligand-binding domain tilts, transmitting rotational torque through the transmembrane alpha-helices (specifically the M2 pore-lining helices). This conformational shift dilates a central gate, creating a water-filled pore that facilitates the passive, electrochemically driven flux of cations—principally sodium (Na+), potassium (K+), and, in certain neuronal subtypes, calcium (Ca2+). This rapid cation influx depolarizes the post-synaptic membrane, generating an excitatory postsynaptic potential (EPSP) or triggering an endplate potential (EPP) sufficient to fire an action potential in skeletal muscle fibers.
Conversely, muscarinic acetylcholine receptors do not form intrinsic ion channels. Instead, they feature seven hydrophobic transmembrane alpha-helices characteristic of the Class A GPCR family. Ligand occupancy within the central transmembrane cavity destabilizes the ground state of the receptor, promoting structural shifts in transmembrane helices 5 and 6 that open an intracellular binding cleft. Heterotrimeric G proteins (Gq/11, Gi/o, or Gs) dock into this intracellular pocket, catalyzing the exchange of guanosine diphosphate (GDP) for guanosine triphosphate (GTP) on the Gα subunit.
The dissociated Gα subunit and Gβγ heterodimer subsequently stimulate or inhibit specific intracellular secondary messenger cascades. Receptors coupled to Gq/11 (M1, M3, M5 subtypes) activate phospholipase C-beta (PLCβ), which hydrolyzes membrane phosphatidylinositol 4,5-bisphosphate into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 mobilizes intracellular calcium stores from the endoplasmic reticulum, while DAG stimulates protein kinase C (PKC). Receptors coupled to Gi/o (M2, M4 subtypes) inhibit adenylyl cyclase, lowering intracellular cyclic adenosine monophosphate (cAMP) levels, while their associated Gβγ subunits directly gate inwardly rectifying potassium channels (GIRK/Kir3) to hyperpolarize excitable cells, such as cardiac pacemaker tissue.
The temporal dynamics of AChR signaling are constrained by enzymatic degradation. To prevent continuous receptor activation and subsequent excitotoxicity or depolarization block, the enzyme acetylcholinesterase (AChE) rapidly hydrolyzes acetylcholine into acetate and choline within fractions of a millisecond. Furthermore, continuous exposure to agonists drives nicotinic and muscarinic receptors into desensitized states, uncoupling ligand binding from ion conduction or downstream G protein activation through intrinsic conformational changes and G protein-coupled receptor kinase (GRK)-mediated phosphorylation.
5. Historical Development
The concept of acetylcholine receptors emerged concurrently with the founding principles of modern pharmacology and chemical synaptic transmission. In 1869, Oswald Schmiedeberg and Richard Koppe observed that muscarine, an alkaloid derived from the fly agaric mushroom (Amanita muscaria), mirrored the physiological consequences of vagal nerve stimulation on the heart, highlighting chemical-specific biological control. In 1905, British physiologist John Newport Langley introduced the foundational concept of a “receptive substance” on skeletal muscle, noting that nicotine stimulated muscle contraction even after surgical denervation had severed neural contacts.
Sir Henry Hallett Dale formalized the dual classification of cholinergic actions in 1914. Dale demonstrated that the synthetic ester acetylcholine replicated both the rapid, curare-sensitive effects of nicotine (the “nicotinic” actions) and the slower, atropine-sensitive cardiac and glandular responses induced by muscarine (the “muscarinic” actions). In 1921, Otto Loewi established the reality of chemical neurotransmission by collecting fluid from a stimulated vagus nerve of a frog heart (termed Vagusstoff) and applying it to an unstimulated heart, producing identical bradycardia; Vagusstoff was subsequently identified chemically as acetylcholine.
The physical isolation and molecular characterization of an acetylcholine receptor occurred in the early 1970s through the pioneering work of Jean-Pierre Changeux, Ricardo Miledi, and colleagues. Leveraging the electric organ of the electric ray (Torpedo marmorata and Torpedo californica)—an anatomical tissue exceptionally enriched in nicotinic receptors—and using snake venom alpha-neurotoxins (such as alpha-bungarotoxin from Bungarus multicinctus) as high-affinity irreversible ligands, Changeux and his team purified the muscle-type nAChR protein. This achievement made the nicotinic acetylcholine receptor the first neurotransmitter receptor ever biochemically isolated.
During the 1980s, Shosaku Numa and his team cloned the complementary DNAs (cDNAs) encoding the individual subunits (α, β, γ, δ) of the Torpedo and mammalian nAChR, unveiling their primary amino acid sequences. Simultaneously, molecular cloning by Edward Peralta and colleagues unmasked five distinct muscarinic receptor genes (m1–m5). In subsequent decades, high-resolution structural biology advanced dramatically. Nigel Unwin utilized electron cryo-microscopy to elucidate the pentameric architecture of the Torpedo receptor at near-atomic resolution, culminating in recent cryo-EM structures of human homomeric α7 and heteromeric α4β2 nAChRs, alongside crystal structures of all five human mAChR subtypes bound to various agonists, antagonists, and allosteric modulators.
6. Theoretical Foundations
The theoretical framework governing acetylcholine receptor function rests upon classical receptor theory, biophysics, and allostery. Primary among these is the Monod-Wyman-Changeux (MWC) model of allosteric transitions, which Jean-Pierre Changeux applied directly to ligand-gated ion channels. According to this model, the nicotinic receptor pre-exists in a dynamic equilibrium among distinct conformational states: resting (basal closed), active (open channel), and desensitized (closed channel with high ligand affinity). Agonists do not mechanically force the channel open; rather, they selectively bind to and stabilize the active conformation, shifting the statistical equilibrium of the ensemble toward channel opening.
Muscarinic receptor mechanics are understood within the framework of the Ternary Complex Model and its modern extensions, including extended ternary complex and cubic ternary complex models. These paradigms explain how the receptor (R), agonist ligand (L), and heterotrimeric G protein (G) interact dynamically. Ligand binding alters the thermodynamic equilibrium between an inactive conformation (R) and an active conformation (R*). In the R* state, the receptor possesses high affinity for both the agonist and the intracellular G protein, facilitating downstream nucleotide exchange.
Furthermore, contemporary GPCR theory integrates the concept of “biased agonism” or “functional selectivity.” At muscarinic receptors, diverse ligands can stabilize unique, receptor-specific conformational intermediates. Consequently, a biased agonist may preferentially stimulate G protein-dependent signaling while sparing beta-arrestin recruitment, or vice versa. This biological principle offers powerful avenues for therapeutic development by dissociating desired pharmacological actions from receptor-mediated adverse effects.
7. Key Components, Types & Dimensions
The acetylcholine receptor superfamily splits broadly into ionotropic (nicotinic) and metabotropic (muscarinic) architectures, each comprising specialized subtypes characterized by unique structural subunits and pharmacological profiles:
- Muscle-Type Nicotinic Receptors (nAChRs): Found at the neuromuscular junction, these pentamers are composed of four distinct polypeptide subunits in a fixed stoichiometry. Adult receptors consist of (α1)2β1δε, whereas embryonic or fetal variants display an (α1)2β1δγ composition. The incorporation of the ε subunit in adult muscle yields a channel with higher unitary conductance and shorter burst durations compared to embryonic channels.
- Neuronal Nicotinic Receptors (nAChRs): Expressed widely throughout the central and peripheral autonomic nervous systems, these receptors assemble as either homopentamers (such as α7, α8, α9) or heteropentamers (combinations of α2–α10 and β2–β4). The α4β2 and α7 assemblies represent the predominant neuronal subtypes. The α7 pentamer features high permeability to calcium ions and desensitizes rapidly, playing central roles in synaptic plasticity, whereas α4β2 heteromers mediate high-affinity nicotine binding, dopamine release, and addictive reinforcement.
- Odd-Numbered Muscarinic Receptors (M1, M3, M5): These metabotropic subtypes couple primarily to the heterotrimeric Gq/11 protein. M1 receptors localize abundantly to the cerebral cortex, hippocampus, and striatum, facilitating long-term potentiation and cognitive processes. M3 receptors are localized on smooth muscle tissues (causing bronchoconstriction, gastrointestinal peristalsis, and detrusor contraction), exocrine glands (driving salivary, lacrimal, and gastric secretions), and vascular endothelial cells (triggering nitric oxide release and subsequent vasodilation). M5 receptors are concentrated within the substantia nigra and ventral tegmental area, regulating dopamine release and cerebral vascular tone.
- Even-Numbered Muscarinic Receptors (M2, M4): These subtypes couple primarily through the pertussis toxin-sensitive Gi/o pathway. M2 receptors predominate in cardiac tissue, specifically within the sinoatrial node, atrioventricular node, and atrial myocardium. Activation of M2 receptors decreases intracellular cAMP and opens GIRK channels, inducing negative chronotropy (reduced heart rate), negative dromotropy (slowed conduction velocity), and negative inotropy (reduced atrial contractile force). M4 receptors localize within the central nervous system, particularly the basal ganglia, acting as autoreceptors and heteroreceptors that modulate striatal dopamine release and motor behavior.
8. Examples & Illustrative Cases
To grasp the clinical and physiological significance of acetylcholine receptors, consider the following real-world scenarios across motor and autonomic physiology:
Case Illustration 1: Autoimmune Myasthenia Gravis. A 34-year-old female presents to an outpatient neurology clinic complaining of progressive bilateral ptosis, diplopia, and difficulty chewing toward the end of the day. Electrophysiological testing using repetitive nerve stimulation reveals a decremental compound muscle action potential (CMAP) response. Serological assay demonstrates high titers of pathogenic autoantibodies directed against the alpha-1 subunit of the muscle-type nAChR. These antibodies induce complement-mediated destruction of the post-junctional folds, cross-link receptors leading to accelerated endocytosis and degradation, and sterically hinder acetylcholine binding. Treatment with the acetylcholinesterase inhibitor pyridostigmine temporarily prolongs acetylcholine availability within the synaptic cleft, restoring muscle strength by increasing the statistical probability of surviving AChR activation.
Case Illustration 2: Organophosphate Toxicity and Muscarinic Overdrive. An agricultural worker is rushed to an emergency department exhibiting extreme diaphoresis, bronchorrhea, bronchospasm, severe bradycardia, miosis, involuntary urination, and skeletal muscle fasciculations. The patient has been exposed to an organophosphate pesticide, which irreversibly phosphorylates and inactivates acetylcholinesterase. Massive, uninhibited accumulation of acetylcholine produces hyperstimulation of both muscarinic and nicotinic receptors. The patient’s life-threatening pulmonary and cardiac symptoms (the classic “SLUDGEM” syndrome: Salivation, Lacrimation, Urination, Defecation, Gastrointestinal distress, Emesis, Miosis) stem directly from overactivation of M2 and M3 receptors. Administration of high-dose atropine, a competitive muscarinic receptor antagonist, rapidly blocks these binding sites to reverse the bradycardia and dry pulmonary secretions.
9. Measurement & Assessment
The functional expression, density, and pathology of acetylcholine receptors are evaluated through an array of electrophysiological, biochemical, and immunological techniques. In clinical diagnostics, myasthenia gravis is routinely diagnosed using radioimmunoassays (RIA) or enzyme-linked immunosorbent assays (ELISA) that quantify circulating serum autoantibodies directed against muscle AChRs. Cell-based assays (CBAs) utilizing human embryonic kidney (HEK293) cells engineered to express clustered adult AChRs have greatly enhanced sensitivity, identifying antibodies in patients previously deemed seronegative.
In experimental neurophysiology, receptor properties are mapped using patch-clamp electrophysiology. Whole-cell and single-channel recording configurations permit direct measurement of picosiemens-level ionic currents passing through individual nicotinic channels. By adjusting holding potentials and extracellular ion compositions, researchers determine single-channel open probability (Po), mean open time, burst duration, conductance, and desensitization kinetics under various ligand concentrations.
Radioligand binding assays utilize high-affinity, selective ligands to determine receptor affinity (equilibrium dissociation constant, Kd) and receptor density (maximal binding capacity, Bmax). Classic radioligands include [3H]-nicotine and [125I]-alpha-bungarotoxin for nicotinic subtypes, and [3H]-quinuclidinyl benzilate ([3H]-QNB) or [3H]-N-methylscopolamine ([3H]-NMS) for muscarinic subtypes. In intact living humans, Positron Emission Tomography (PET) imaging utilizing tracers such as [18F]-flubatine or [11C]-nicotine visualizes spatial alterations in central α4β2 nAChR density across neurodegenerative conditions like Alzheimer’s disease.
10. Applications & Practical Significance
The wide distribution of acetylcholine receptors throughout the nervous system makes them prime targets for therapeutic intervention across diverse medical disciplines:
Anesthesiology and Surgery: Neuromuscular blocking agents (NMBAs) act specifically upon muscle-type nAChRs to produce skeletal muscle paralysis during endotracheal intubation and major surgical procedures. Depolarizing blockers, such as succinylcholine, act as persistent agonists that initially open nAChR channels, producing fasciculations, followed by a persistent depolarization block that renders muscle fibers electrically excitable. Non-depolarizing blockers, including rocuronium and vecuronium, function as competitive antagonists, preventing acetylcholine from binding and thereby inducing flaccid paralysis.
Pulmonology: In chronic obstructive pulmonary disease (COPD) and acute asthma exacerbations, inhaled muscarinic receptor antagonists serve as first-line bronchodilators. Short-acting muscarinic antagonists (SAMAs, such as ipratropium bromide) and long-acting muscarinic antagonists (LAMAs, such as tiotropium bromide) competitively block post-junctional M3 receptors on bronchial smooth muscle. This inhibition blocks Gq-coupled intracellular calcium mobilization, relaxing airway smooth muscle and reducing mucus hypersecretion.
Psychiatry and Smoking Cessation: Varenicline, an effective pharmacotherapy for tobacco dependence, acts as a high-affinity partial agonist at neuronal α4β2 nicotinic acetylcholine receptors. By binding to these receptors within the mesolimbic dopamine pathway, varenicline provides moderate dopamine release sufficient to alleviate nicotine withdrawal symptoms and cravings, while simultaneously acting as a competitive inhibitor that blocks exogenous nicotine from inducing intense reward spikes.
11. Research & Empirical Evidence
Extensive clinical and preclinical studies have characterized the operational dynamics of AChRs across normal cognitive processing and disease pathophysiology. Foundational research during the 1970s and 1980s by David Bowen, Peter Davies, and colleagues established the “cholinergic hypothesis of Alzheimer’s disease.” Post-mortem examinations demonstrated marked degeneration of cholinergic projection neurons originating within the basal forebrain (nucleus basalis of Meynert) that innervate the neocortex and hippocampus, alongside severe loss of both pre-synaptic and post-synaptic nicotinic receptors. These findings led to the development of acetylcholinesterase inhibitors (donepezil, rivastigmine, galantamine), which increase synaptic acetylcholine residence time and modestly preserve cognitive functions in mild-to-moderate dementia.
Further work by Marina Picciotto and colleagues utilizing knock-out mouse models demonstrated that deletion of the β2 subunit of the nAChR abolished high-affinity nicotine binding and extinguished voluntary nicotine self-administration. This definitively established α4β2-containing nAChRs as the primary molecular substrate mediating nicotine reward and dependence. In schizophrenia research, clinical trials have focused on α7 nAChR positive allosteric modulators (PAMs) following discoveries that polymorphisms in the CHRNA7 gene region correlate with auditory sensory gating deficits (P50 inhibition defects) characteristic of the disorder.
Recent breakthroughs in structural biology have resolved critical questions regarding receptor activation. In 2018, cryo-EM studies published by Ryan Hibbs and colleagues captured the human α4β2 nAChR in both basal, unliganded states and active, nicotine-bound states at near-atomic resolution. These structural models illuminated how nicotine binding reorients the “loop C” region of the alpha subunit, transmitting a downward mechanical pull that rocks the M2 transmembrane helices outward to widen the ion channel pore.
12. Cultural & Cross-Cultural Considerations
The cultural history of human societies has long been intertwined with natural alkaloids that target acetylcholine receptors, often preceding modern scientific understanding by centuries. Indigenous peoples throughout the Americas cultivated and consumed Nicotiana tabacum for ceremonial, spiritual, and social purposes, unwittingly harnessing the affinity of nicotine for neuronal α4β2 and α7 nAChRs to elevate dopamine, increase alertness, and suppress appetite.
Similarly, the use of plants containing belladonna alkaloids—such as Atropa belladonna (deadly nightshade), Hyoscyamus niger (henbane), and Datura stramonium—has deep roots in European, South Asian, and Middle Eastern folklore, medicine, and spiritual rituals. The name belladonna (“beautiful lady” in Italian) derives from the Renaissance practice in which women instilled drops of plant extract into their eyes to induce mydriasis (pupillary dilation) by blocking ocular M3 receptors, an aesthetic marker of beauty at the time. In traditional hunting cultures across the Amazon basin, indigenous hunters coated blowdarts with curare (derived from Chondrodendron tomentosum), using its active constituent, tubocurarine, to paralyze prey by competitively blocking muscle-type nAChRs.
13. Criticisms, Debates & Limitations
Despite decades of intense investigation, therapeutic drug development targeting the acetylcholine receptor family faces notable hurdles, primarily due to structural homology across subtypes. Because the orthosteric binding pockets of the five muscarinic subtypes (M1–M5) exhibit extreme sequence conservation, developing small molecules that selectively target one subtype without inducing adverse effects through others has proven exceedingly difficult. For example, early attempts to treat Alzheimer’s disease with M1 agonists were abandoned because concomitant activation of peripheral M2 and M3 receptors caused severe, dose-limiting cholinergic toxicity, including nausea, vomiting, abdominal cramping, and profound bradycardia.
To overcome this limitation, pharmaceutical research shifted focus from orthosteric agonists toward positive allosteric modulators (PAMs). Allosteric binding pockets are located outside the primary active site, where sequence divergence among receptor subtypes is far greater, enabling far higher subtype selectivity. However, challenges remain concerning allosteric cooperativity, probe dependence, and delayed desensitization or internalization kinetics.
Another longstanding debate involves the viability of the cholinergic hypothesis in psychiatric illness. Early formulations posited that balancing cholinergic and dopaminergic signaling represented the central therapeutic target in disorders like schizophrenia. However, clinical trials evaluating selective α7 agonists have shown mixed outcomes, often failing to demonstrate durable, clinically meaningful improvements in cognitive endpoints, likely due to rapid receptor desensitization and complex compensatory network dynamics across broader circuitries.
14. Related Terms & Distinctions
To prevent conceptual confusion, the acetylcholine receptor must be distinguished from several related neurochemical components and receptor families:
- Acetylcholinesterase (AChE): While an AChR is a membrane receptor that transduces signals upon binding acetylcholine, AChE is a high-turnover hydrolase enzyme located in the synaptic cleft responsible for clearing acetylcholine through enzymatic cleavage into choline and acetate.
- Adrenergic Receptors: Receptors that bind catecholamines (epinephrine and norepinephrine). Although adrenergic and muscarinic receptors both belong to the GPCR superfamily, they mediate opposing branches of the autonomic nervous system in many organ systems (sympathetic vs. parasympathetic control).
- Choline Acetyltransferase (ChAT): The presynaptic biosynthetic enzyme that synthesizes acetylcholine from acetyl-CoA and choline, distinct from the post-synaptic receptors that detect the released neurotransmitter.
- GABAA Receptors: Structurally related pentameric ligand-gated ion channels belonging to the same Cys-loop superfamily as nAChRs. However, while nAChRs are non-selective cation channels that depolarize cells to produce excitation, GABAA receptors are chloride-selective anion channels that hyperpolarize cells to mediate inhibitory neurotransmission.
- Muscarinic vs. Nicotinic Receptors: A fundamental distinction within the AChR category: nicotinic receptors are fast-acting, ionotropic pentamers permeable to cations, whereas muscarinic receptors are slow-acting, metabotropic GPCRs operating through intracellular second messenger cascades.
15. Summary / Key Takeaways
The acetylcholine receptor constitutes an indispensable molecular gateway governing neuromuscular execution, autonomic equilibrium, and central cognitive integration. Divided into fast-acting, ionotropic nicotinic pentamers and slower, metabotropic muscarinic GPCRs, these receptors convert presynaptic chemical exocytosis into complex electrical and biochemical signals. From its historic role as the first purified neurotransmitter receptor to its clinical centrality in myasthenia gravis, chronic pulmonary disease, anesthesia, and neuropsychiatric disorders, the acetylcholine receptor remains a cornerstone of molecular neurobiology and translational pharmacology.
References
- Changeux, J. P. (2012). The nicotinic acetylcholine receptor: The founding father of the pentameric ligand-gated ion channel superfamily. Journal of Biological Chemistry, 287(48), 40207–40215. https://doi.org/10.1074/jbc.R112.407668
- Dale, H. H. (1914). The action of certain esters and ethers of choline, and their relation to muscarine. Journal of Pharmacology and Experimental Therapeutics, 6(2), 147–190.
- Kruse, A. C., Kobilka, B. K., Gautam, D., Sexton, P. M., Christopoulos, A., & Wess, J. (2014). Muscarinic acetylcholine receptors: Novel opportunities for drug development. Nature Reviews Drug Discovery, 13(7), 549–560. https://doi.org/10.1038/nrd4295
- Unwin, N. (2005). Refined structure of the nicotinic acetylcholine receptor at 4Å resolution. Journal of Molecular Biology, 346(4), 967–989. https://doi.org/10.1016/j.jmb.2004.12.031
- Walsh, C. T., & Changeux, J. P. (2018). The nicotinic acetylcholine receptor: From pioneering pharmacology to atomic structure. Neuropharmacology, 132, 1–6. https://doi.org/10.1016/j.neuropharm.2017.12.030