scholarly journals Membrane-related specializations associated with acetylcholine receptor aggregates induced by electric fields.

1985 ◽  
Vol 100 (1) ◽  
pp. 235-244 ◽  
Author(s):  
P W Luther ◽  
H B Peng
Keyword(s):  
Acetylcholine Receptor ◽  
Electric Fields ◽  
Basal Lamina ◽  
Field Exposure ◽  
Thin Sections ◽  
Fluorescence Image ◽  
Before And After ◽  
Dc Electric Field ◽  
Receptor Clusters ◽  
Alpha Bungarotoxin

The localization of membrane-associated specializations (basal lamina and cytoplasmic density) at sites of acetylcholine receptor (AChR) aggregation is consistent with an involvement of these structures in receptor stabilization. We investigated the occurrence of these specializations in association with AChR aggregates that develop at the cathode-facing edge of Xenopus muscle cells during exposure to a DC electric field. The cultures were labeled with a fluorescent conjugate of alpha-bungarotoxin and the receptor distribution on selected cells was determined before and after exposure to the field. In thin sections taken from the same cells, the cathode-facing edge was characterized by plaques of basal lamina and cytoplasmic density co-extensive with sarcolemma of increased density. In sections cut in a plane similar to the fluorescence image, it was possible to demonstrate that the specializations were concentrated at areas of field-induced AChR aggregation, and at receptor clusters existing on control cells. This finding further indicates that these structures participate in AChR stabilization, and that the mechanisms involved in AChR aggregation that result from field exposure and nerve contact may be similar.

scholarly journals Disruption and reformation of the acetylcholine receptor clusters of cultured rat myotubes occur in two distinct stages.

1987 ◽  
Vol 104 (1) ◽  
pp. 97-108 ◽  
Author(s):  
D W Pumplin ◽  
R J Bloch
Keyword(s):  
Acetylcholine Receptor ◽  
Freeze Fracture ◽  
Bright Spots ◽  
Step Model ◽  
Before And After ◽  
Control Myotubes ◽  
Internalization Rate ◽  
Receptor Clusters ◽  
Alpha Bungarotoxin ◽  
Fixed Array

We have examined the redistribution of acetylcholine receptor (AChR) intramembrane particles (IMPs) when AChR clusters of cultured rat myotubes are experimentally disrupted and allowed to reform. In control myotubes, the AChR IMPs are evenly distributed within the AChR domains of cluster membrane. Shortly after addition of azide to disrupt clusters, IMPs become unevenly scattered, with some microaggregation. After longer treatment, IMPs are depleted from AChR domains with no further change in IMP distribution. Contact domains of clusters are relatively poor in IMPs both before and after cluster dispersal. Upon visualization with fluorescent alpha-bungarotoxin, some AChR in azide-treated samples appear as small, bright spots. These spots do not correspond to microaggregates seen in freeze-fracture replicas, and probably represent receptors that have been internalized. The internalization rate is insufficient to account completely for the loss of IMPs from clusters, however. During reformation of AChR clusters upon removal of azide, IMP concentration in receptor domains increases. At early stages of reformation, IMPs appear in small groups containing compact microaggregates. At later times, AChR domains enlarge and IMPs within them assume the evenly spaced distribution characteristic of control clusters. These observations suggest that the disruption of clusters is accompanied by mobilization of AChR from a fixed array, allowing AChR IMPs to diffuse away from the clusters, to form microaggregates, and to become internalized. Cluster reformation appears to be the reverse of this process. Our results are thus consistent with a two-step model for AChR clustering, in which the concentration of IMPs into a small membrane region precedes their rearrangement into evenly spaced sites.

Basal lamina components are concentrated in premuscle masses and at early acetylcholine receptor clusters in chick embryo hindlimb muscles

1988 ◽  
Vol 130 (2) ◽  
pp. 471-486 ◽  
Author(s):  
Earl W. Godfrey ◽  
Ruth E. Siebenlist ◽  
Peter A. Wallskog ◽  
Linda M. Walters ◽  
David L. Bolender ◽  
...  
Keyword(s):  
Chick Embryo ◽  
Acetylcholine Receptor ◽  
Basal Lamina ◽  
Hindlimb Muscles ◽  
Receptor Clusters

scholarly journals Freeze-fracture and electrophysiological studies of newly developed acetylcholine receptors in Xenopus embryonic muscle cells.

1984 ◽  
Vol 98 (6) ◽  
pp. 2160-2173 ◽  
Author(s):  
P C Bridgman ◽  
S Nakajima ◽  
A S Greenberg ◽  
Y Nakajima
Keyword(s):  
Size Distribution ◽  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Freeze Fracture ◽  
Muscle Cells ◽  
Embryonic Muscle ◽  
Freeze Fracture Electron Microscopy ◽  
Receptor Clusters ◽  
Alpha Bungarotoxin ◽  
Solitary Form

The development of acetylcholine receptors on Xenopus embryonic muscle cells both in culture and in situ was studied using electrophysiology and freeze-fracture electron microscopy. Acetylcholine sensitivity first appeared at developmental stage 20 and gradually increased up to about stage 31. Freeze-fracture of muscle cells that were nonsensitive to acetylcholine revealed diffusely distributed small P-face intramembraneous particles. When cells acquired sensitivity to acetylcholine, a different group of diffusely distributed large P-face particles began to appear. This group of particles was analyzed by subtracting the size distribution found on nonsensitive cells from that found on sensitive cells. We call this group of particles difference particles. The sizes of difference particles were large (peak diameter 11 nm). The density of difference particles gradually increased with development. The density of small particles (less than 9 nm) did not change with development. At later stages (32-36) aggregates of large particles appeared, which probably represent acetylcholine receptor clusters. The size distribution of difference particles was close to that of the aggregated particles, suggesting that at least part of difference particles represent diffusely distributed acetylcholine receptors. Difference particles exist mostly in solitary form (occasionally double), indicating that an acetylcholine receptor can be functional in solitary form. This result also shows that diffuse acetylcholine receptors that have previously been observed with 125I-alpha-bungarotoxin autoradiography do indeed exist in solitary forms not as microaggregates.

scholarly journals Localization of intracellular proteins at acetylcholine receptor clusters induced by electric fields in Xenopus muscle cells

1989 ◽  
Vol 94 (1) ◽  
pp. 73-83
Author(s):  
M.W. Rochlin ◽  
H.B. Peng
Keyword(s):  
Electric Field ◽  
Acetylcholine Receptor ◽  
Electric Fields ◽  
Matrix Material ◽  
Muscle Cells ◽  
Ultrastructural Level ◽  
Anchoring Proteins ◽  
Intracellular Proteins ◽  
Receptor Clusters ◽  
Electric Field Treatment

Electric fields cause acetylcholine receptor (AChR) patches to form on the cathodal sides of cultured muscle cells. These patches are stable for several hours following cessation of an electric field treatment, indicating that the receptors are anchored to the cluster sites. Furthermore, at the ultrastructural level, AChR patches induced by electric fields are marked by an accumulation of extracellular matrix material and a sarcolemmal density. Thus, these AChR patches are similar to those induced by other stimuli, including nerve, polycation-coated beads, and the tissue culture substratum. Proteins that may be involved in anchoring AChRs have been colocalized with AChR patches induced by the latter three stimuli, but not at AChR patches induced by electric fields. In this study, we demonstrate that three putative anchoring proteins, 43K (K = 10(3) Mr) protein, 58K protein and talin, are associated with field-induced AChR patches. We also show that these proteins persist at field-induced AChR patches following removal of the field, indicating that they are stabilized at the AChR patch. Our data are consistent with the possibility that these proteins contribute to the stabilization of AChRs at patches induced by the electric field. Since 43K, 58K and talin are intracellular proteins, and therefore could not undergo field-induced lateral electrophoresis, our observations support the notion that the electric field triggers the formation of an AChR-stabilizing specialization.

scholarly journals Early events in neuromuscular junction formation in vitro: induction of acetylcholine receptor clusters in the postsynaptic membrane and morphology of newly formed synapses.

1979 ◽  
Vol 83 (1) ◽  
pp. 143-158 ◽  
Author(s):  
E Frank ◽  
G D Fischbach
Keyword(s):  
Synapse Formation ◽  
Synaptic Cleft ◽  
Postsynaptic Membrane ◽  
Active Growth ◽  
Before And After ◽  
Nerve Muscle ◽  
Scanning Em ◽  
Receptor Clusters ◽  
Alpha Bungarotoxin

The development of clusters of acetylcholine (ACh) receptors at newly formed synapses between embryonic chick spinal cord and muscle cells grown in vitro has been studied by iontophoretic mapping with ACh. A semi-automated technique using on-line computer analysis of ACh responses and a photographic system to record the position of each ACh application permit the rapid construction of extensive and detailed maps of ACh sensitivity. Clusters of receptors, evident as peaks of ACh sensitivity, are present on many uninnervated myotubes. The distribution of ACh sensitivity closely parallels the distribution of 125I-alpha-bungarotoxin binding sites on the same muscle cell. In all cases where individual myotubes were adequately mapped before and after synapse formation, ingrowing axons induced new clusters of receptors rather than seeking out preexisting clusters. Synapses can form at active growth cones within 3 h of nerve-muscle contact. New receptor clusters can appear beneath neurites within a few hours. Many of the uninnervated clusters on innervated myotubes disappear with time. In contrast, receptor clusters on uninnervated myotubes remain in the same location for many hours. Synaptic clusters and clusters on uninervated myotubes are stable even though individual receptors are metabolized rapidly. The morphology of several identified sites of transmitter release was examined. At the scanning EM level, synapses appeared as small, rough-surfaced varicosities with filopodia that radiated outwards over the muscle surface. One synapse was studied by transmission EM. Acetylcholinesterase and a basement lamina were present within the synaptic cleft.

scholarly journals Distribution of filipin-sterol complexes on cultured muscle cells: cell-substratum contact areas associated with acetylcholine receptor clusters.

1983 ◽  
Vol 96 (2) ◽  
pp. 363-372 ◽  
Author(s):  
P C Bridgman ◽  
Y Nakajima
Keyword(s):  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Freeze Fracture ◽  
Muscle Cells ◽  
Distinct Pattern ◽  
Intramembrane Particles ◽  
Membrane Topography ◽  
Interference Contrast Microscopy ◽  
Receptor Clusters ◽  
Alpha Bungarotoxin

Specialized areas within broad, close, cell-substratum contacts seen with reflection interference contrast microscopy in cultures of Xenopus embryonic muscle cells were studied. These areas usually contained a distinct pattern of light and dark spots suggesting that the closeness of apposition between the membrane and the substratum was irregular. They coincided with areas containing acetylcholine receptor clusters identified by fluorescence labeled alpha-bungarotoxin. Freeze-fracture of the cells confirmed these observations. The membrane in these areas was highly convoluted and contained aggregates of large P-face intramembrane particles (probably representing acetylcholine receptors). If cells were fixed and then treated with the sterol-specific antibiotic filipin before fracturing, the pattern of filipin-sterol complex distribution closely followed the pattern of cell-substratum contact. Filipin-sterol complexes were in low density in the regions where the membrane contained clustered intramembrane particles. These membrane regions were away from the substratum (bright white areas in reflection interference contrast; depressions of the P-face in freeze-fracture). Filipin-sterol complexes were also in reduced density where the membrane was very close to the substratum (dark areas in reflection interference contrast; bulges of the P-face in freeze-fracture). These areas were not associated with clustered acetylcholine receptors (aggregated particles). This result suggests that filipin treatment causes little or no artefact in either acetylcholine receptor distribution or membrane topography of fixed cells and that the distribution of filipin-sterol complexes may closely parallel the microheterogeneity of membranes that exist in living cells.

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
Sign in / Sign up

Export Citation Format

Share Document