Disorders of the neuromuscular junction

2010 ◽  
pp. 5177-5184 ◽  
Author(s):  
David Hilton-Jones ◽  
Jacqueline Palace
Keyword(s):  
Ion Channels ◽  
Neuromuscular Junction ◽  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Muscle Receptor ◽  
Male Preponderance ◽  
Female Bias ◽  
Anti Acetylcholine

Two fundamentally different pathological processes are associated with disease at the neuromuscular junction: (1) acquired disorders in which autoantibodies are directed against nerve or muscle receptor or ion channels; (2) rare inherited conditions in which the defect may be pre- or postsynaptic. Aetiology and epidemiology—the fundamental disorder is loss of functional acetylcholine receptors most frequently as a result of binding of anti-acetylcholine receptor (anti-AChR) antibodies. Incidence is about 10 per million population and prevalence about 8 per 100 000, with a marked female bias in cases aged under 40 years and male preponderance in those over 50 years. Thymomas occur in about 10% of cases....

Disorders of the neuromuscular junction

2020 ◽  
pp. 6295-6303
Author(s):  
David Hilton-Jones ◽  
Jacqueline Palace
Keyword(s):  
Ion Channels ◽  
Neuromuscular Junction ◽  
Peripheral Nerve ◽  
Acetylcholine Receptor ◽  
Nerve Terminal ◽  
Small Region ◽  
Autoimmune Disorders ◽  
Inherited Disorders ◽  
Pathogenic Mechanisms ◽  
Muscle Receptor

This chapter looks at how two fundamentally different pathological processes are associated with disease at the neuromuscular junction: acquired disorders in which autoantibodies are directed against nerve or muscle receptor or ion channels; rare inherited conditions in which the defect may be pre- or postsynaptic. The acquired neuromuscular junction disorders are associated with antibodies directed against one of the ion channels. The fact that there are three autoimmune disorders known to affect such a small region may be explained by the neuromuscular junction, unlike the peripheral nerve, not being contained within the blood–nerve barrier, which stops just short of the nerve terminal, and thus being potentially exposed to circulating humoral attack. The inherited disorders may affect presynaptic processes (acetylcholine resynthesis, packaging, or release), acetylcholinesterase binding, or postsynaptic function (acetylcholine receptor numbers or localization). Pathogenic mechanisms are considered in more detail when discussing individual disorders.

scholarly journals Ancestral acetylcholine receptor β-subunit forms homopentamers that prime before opening spontaneously

2022 ◽  
Author(s):  
Christian J.G. Tessier ◽  
R. Michel Sturgeon ◽  
Johnathon R. Emlaw ◽  
Gregory D. McCluskey ◽  
F. Javier Pérez-Areales ◽  
...  
Keyword(s):  
Ion Channels ◽  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Common Ancestor ◽  
Single Channel ◽  
Receptor Activity ◽  
Β Subunit ◽  
Receptor Function ◽  
Muscle Type ◽  
Α Subunits

Human adult muscle-type acetylcholine receptors are heteropentameric ion channels formed from two α-subunits, and one each of the β-, δ-, and ϵ- subunits. To form functional channels, the subunits must assemble with one another in a precise stoichiometry and arrangement. Despite being different, the four subunits share a common ancestor that is presumed to have formed homopentamers. The extent to which the properties of the modern-day receptor result from its subunit complexity is unknown. Here we show that a reconstructed ancestral muscle-type β-subunit can form homopentameric ion channels. These homopentamers open spontaneously and display single-channel hallmarks of muscle type acetylcholine receptor activity. Our findings demonstrate that signature features of muscle-type acetylcholine receptor function are independent of agonist, and do not necessitate the complex heteropentameric architecture of the modern-day receptor.

scholarly journals Immunoelectron microscopy of acetylcholine receptors and 43 KD protein after rapid freezing, freeze-substitution, and low-temperature embedding in lowicryl K11M.

1991 ◽  
Vol 39 (5) ◽  
pp. 625-634 ◽  
Author(s):  
G W Phillips ◽  
P C Bridgman
Keyword(s):  
Monoclonal Antibodies ◽  
Low Temperature ◽  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Uv Light ◽  
Freeze Substitution ◽  
Rapid Freezing ◽  
Cytoplasmic Surface ◽  
Cytoplasmic Proteins ◽  
Anti Acetylcholine

To label intracellular determinants of the acetylcholine receptor and associated cytoplasmic proteins while preserving optimal ultrastructure, we developed a post-embedment labeling technique that uses rapid-frozen specimens and freeze-substitution without chemical fixatives. This procedure has been made possible through the use of a low-temperature resin (Lowicryl K11M) that can be polymerized with UV light at -60 degrees C. Rapid-frozen muscle cells were used to evaluate the preservation of structure, and Torpedo electroplaque cells and purified postsynaptic membranes were used to quantitatively evaluate the labeling specificity, efficiency, and resolution of the technique. The labeling efficiency of seven different monoclonal antibodies (MAb) to the acetylcholine receptor varied from 3-13%; there was a correlation between the degree of efficiency and the number of epitopes with which the antibodies reacted. The resolution of the technique was not sufficient to determine whether the anti-acetylcholine receptor MAb were bound to the cytoplasmic or the extracellular surface, but was sufficient to correctly determine the location of the receptor-associated 43 KD protein on the cytoplasmic surface.

scholarly journals The mechanism of agrin-induced acetylcholine receptor aggregation

1991 ◽  
Vol 331 (1261) ◽  
pp. 273-280 ◽  
Keyword(s):  
Neuromuscular Junction ◽  
Tyrosine Phosphorylation ◽  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Neuromuscular Junctions ◽  
Electric Organ ◽  
Motor Axon ◽  
Β Subunit ◽  
Axon Terminals ◽  
Receptor Aggregation

Agrin, a protein isolated from the synapse-rich electric organ of Torpedo californica , induces the formation of specializations on myotubes in culture which resemble the post-synaptic apparatus at the vertebrate skeletal neuromuscular junction. For example, the specializations contain aggregates of acetylcholine receptors and acetylcholinesterase. This report summarizes the evidence that the formation of the postsynaptic apparatus at developing and regenerating neuromuscular junctions is triggered by the release of agrin from motor axon terminals and describes results of recent experiments which suggest that agrininduced tyrosine phosphorylation of the β subunit of the acetylcholine receptor may play a role in receptor aggregation.

scholarly journals Characterisation of alpha-dystrobrevin in muscle

1998 ◽  
Vol 111 (17) ◽  
pp. 2595-2605 ◽  
Author(s):  
R. Nawrotzki ◽  
N.Y. Loh ◽  
M.A. Ruegg ◽  
K.E. Davies ◽  
D.J. Blake
Keyword(s):  
Skeletal Muscle ◽  
Neuromuscular Junction ◽  
Cell Surface ◽  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Synapse Formation ◽  
Electric Organ ◽  
Postsynaptic Membrane ◽  
Related Protein ◽  
Receptor Clustering

Dystrophin-related and associated proteins are important for the formation and maintenance of the mammalian neuromuscular junction. Initial studies in the electric organ of Torpedo californica showed that the dystrophin-related protein dystrobrevin (87K) co-purifies with the acetylcholine receptors and other postsynaptic proteins. Dystrobrevin is also a major phosphotyrosine-containing protein in the postsynaptic membrane. Since inhibitors of tyrosine protein phosphorylation block acetylcholine receptor clustering in cultured muscle cells, we examined the role of alpha-dystrobrevin during synapse formation and in response to agrin. Using specific antibodies, we show that C2 myoblasts and early myotubes only produce alpha-dystrobrevin-1, the mammalian orthologue of Torpedo dystrobrevin, whereas mature skeletal muscle expresses three distinct alpha-dystrobrevin isoforms. In myotubes, alpha-dystrobrevin-1 is found on the cell surface and also in acetylcholine receptor-rich domains. Following agrin stimulation, alpha-dystrobrevin-1 becomes re-localised beneath the cell surface into macroclusters that contain acetylcholine receptors and another dystrophin-related protein, utrophin. This redistribution is not associated with tyrosine phosphorylation of alpha-dystrobrevin-1 by agrin. Furthermore, we show that alpha-dystrobrevin-1 is associated with both utrophin in C2 cells and dystrophin in mature skeletal muscle. Thus alpha-dystrobrevin-1 is a component of two protein complexes in muscle, one with utrophin at the neuromuscular junction and the other with dystrophin at the sarcolemma. These results indicate that alpha-dystrobrevin-1 is not involved in the phosphorylation-dependent, early stages of receptor clustering, but rather in the stabilisation and maturation of clusters, possibly via an interaction with utrophin.

Nonhalogenated Alkane Anesthetics Fail to Potentiate Agonist Actions on Two Ligand-gated Ion Channels

2001 ◽  
Vol 95 (2) ◽  
pp. 470-477 ◽  
Author(s):  
Douglas E. Raines ◽  
Robert J. Claycomb ◽  
Michaela Scheller ◽  
Stuart A. Forman
Keyword(s):  
Ion Channels ◽  
Acetylcholine Receptor ◽  
Nicotinic Acetylcholine Receptor ◽  
Nicotinic Acetylcholine Receptors ◽  
Acetylcholine Receptors ◽  
Nicotinic Acetylcholine ◽  
Gaba A ◽  
Agonist Affinity ◽  
Gated Ion Channels ◽  
Ligand Gated Ion Channels

Background Although ether, alcohol, and halogenated alkane anesthetics potentiate agonist actions or increase the apparent agonist affinity of ligand-gated ion channels at clinically relevant concentrations, the effects of nonhalogenated alkane anesthetics on ligand-gated ion channels have not been studied. The current study assessed the abilities of two representative nonhalogenated alkane anesthetics (cyclopropane and butane) to potentiate agonist actions or increase the apparent agonist affinity of two representative ligand-gated ion channels: the nicotinic acetylcholine receptor and y-aminobutyric acid type A (GABA(A)) receptor. Methods Nicotinic acetylcholine receptors were obtained from the electroplax organ of Torpedo nobiliana, and human GABA(A) receptors (alpha1beta2gamma2L) were expressed in human embryonic kidney 293 cells. The Torpedo nicotinic acetylcholine receptors apparent agonist affinity in the presence and absence of anesthetic was assessed by measuring the apparent rates of desensitization induced by a range of acetylcholine concentrations. The GABA(A) receptor's apparent agonist affinity in the presence and absence of anesthetic was assessed by measuring the peak currents induced by a range of GABA concentrations. Results Neither cyclopropane nor butane potentiated agonist actions or increased the apparent agonist affinity (reduced the apparent agonist dissociation constant) of the Torpedo nicotinic acetylcholine receptor or GABA(A) receptor. At clinically relevant concentrations, cyclopropane and butane reduced the apparent rate of Torpedo nicotinic acetylcholine receptor desensitization induced by low concentrations of agonist. Conclusions Our results suggest that the in vivo central nervous system depressant effects of nonhalogenated alkane anesthetics do not result from their abilities to potentiate agonist actions on ligand-gated ion channels. Other targets or mechanisms more likely account for the anesthetic activities of nonhalogenated alkane anesthetics.

scholarly journals Identification of agrin in electric organ extracts and localization of agrin-like molecules in muscle and central nervous system

1987 ◽  
Vol 132 (1) ◽  
pp. 223-230 ◽  
Author(s):  
M. A. Smith ◽  
Y. M. Yao ◽  
N. E. Reist ◽  
C. Magill ◽  
B. G. Wallace ◽  
...  
Keyword(s):  
Neuromuscular Junction ◽  
Acetylcholine Receptor ◽  
Basal Lamina ◽  
Acetylcholine Receptors ◽  
Electric Organ ◽  
Synaptic Cleft ◽  
Muscle Fibres ◽  
Motor Neurones ◽  
Cultured Myotubes ◽  
Torpedo Electric Organ

The portion of the muscle fibre's basal lamina that occupies the synaptic cleft at the neuromuscular junction contains molecules that cause the aggregation of acetylcholine receptors and acetylcholinesterase on regenerating muscle fibres. Agrin, which is extracted from basal lamina-containing fractions of the Torpedo electric organ and causes the formation of acetylcholine receptor and acetylcholinesterase aggregates on cultured myotubes, may be similar, if not identical, to the acetylcholine receptor- and acetylcholinesterase-aggregating molecules at the neuro-muscular junction. Here we summarize experiments which led to the identification of agrin and established that the basal lamina at the neuromuscular junction contains molecules antigenically similar to agrin. We also discuss results which raise the possibility that agrin-like molecules at the neuromuscular junction are produced by motor neurones.

scholarly journals CLASP2-dependent microtubule capture at the neuromuscular junction membrane requires LL5β and actin for focal delivery of acetylcholine receptor vesicles

2015 ◽  
Vol 26 (5) ◽  
pp. 938-951 ◽  
Author(s):  
Sreya Basu ◽  
Stefan Sladecek ◽  
Isabel Martinez de la Peña y Valenzuela ◽  
Mohammed Akaaboune ◽  
Ihor Smal ◽  
...  
Keyword(s):  
Neuromuscular Junction ◽  
Actin Cytoskeleton ◽  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Postsynaptic Membrane ◽  
Interaction Partner ◽  
Synaptic Membrane ◽  
Microtubule Capture

A novel mechanism is described for the agrin-mediated focal delivery of acetylcholine receptors (AChRs) to the postsynaptic membrane of the neuromuscular junction. Microtubule capture mediated by CLASP2 and its interaction partner, LL5β, and an intact subsynaptic actin cytoskeleton are both required for focal AChR transport to the synaptic membrane.

scholarly journals Might prepatterned acetylcholine-receptor clusters on surface myotubes be a sign of neuromuscular-junction maturation failure?

2013 ◽  
Vol 4 ◽  
pp. 319-323
Author(s):  
Anna Fidziańska ◽  
Maria Jędrzejowska ◽  
Agnieszka Madej-Pilarczyk ◽  
Jacek Bojakowski
Keyword(s):  
Neuromuscular Junction ◽  
Acetylcholine Receptor ◽  
Receptor Clusters
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