scholarly journals Participation of calcium and calmodulin in the formation of acetylcholine receptor clusters.

1984 ◽  
Vol 98 (2) ◽  
pp. 550-557 ◽  
Author(s):  
H B Peng
Keyword(s):  
Acetylcholine Receptor ◽  
Divalent Cations ◽  
Simple Procedure ◽  
Latex Beads ◽  
Immunofluorescence Studies ◽  
Cellular Machinery ◽  
The Stability ◽  
Receptor Clusters ◽  
Myotomal Muscle ◽  
Achr Clustering

The formation of acetylcholine receptor (AChR) clusters can be experimentally induced in cultured Xenopus myotomal muscle cells by positive polypeptide-coated latex beads (Peng, H.B., P.-C. Cheng, and P.W. Luther, 1981, Nature [Lond.], 292:831-834). This provides a simple procedure for studying the cellular process of AChR clustering. In this study, the involvement of calcium and calmodulin in this process was examined. A deprivation in extracellular calcium by calcium-free medium or by the addition of calcium antagonists such as divalent cations Co2+ and Ni2+ (1-5 mM) or organic compounds verapamil and D-600 (0.1-0.5 mM) suppressed the formation of AChR clusters induced by the latex beads in a largely reversible manner. Antagonists against calmodulin, including trifluoperazine (1-5 microM) and the naphthalene sulfonamide W-7 (20 microM), also suppressed AChR clustering. However, the effect of W-7 was much weaker than that of trifluoperazine (TFP). Although the formation of AChR clusters is inhibited by these drugs, the stability of the existent clusters is relatively insensitive to them. These data suggest that the clustering of AChR involves a Ca2+ and calmodulin-activated process. Immunofluorescence studies using an antibody against calmodulin indicate that calmodulin is diffusely distributed in the cytoplasm in addition to its localization at the I-bands. Thus I propose that a local rise in intracellular calcium caused by a locally applied stimulus, exemplified here by the polypeptide-coated latex beads, may trigger the formation of AChR clusters. Furthermore, the cellular machinery for this process may involve calmodulin and is diffusely distributed in the muscle cell.

scholarly journals Early cytoplasmic specialization at the presumptive acetylcholine receptor cluster: a meshwork of thin filaments.

1984 ◽  
Vol 99 (1) ◽  
pp. 344-349 ◽  
Author(s):  
H B Peng ◽  
K A Phelan
Keyword(s):  
Acetylcholine Receptor ◽  
Time Course ◽  
Smooth Endoplasmic Reticulum ◽  
Thin Filaments ◽  
Latex Beads ◽  
Cluster A ◽  
Postsynaptic Differentiation ◽  
Myotomal Muscle ◽  
Acetylcholine Receptor Cluster ◽  
Achr Clustering

Postsynaptic differentiation can be experimentally induced in cultured Xenopus myotomal muscle cells by polyornithine-coated latex beads (Peng, H. B., and P.-C. Cheng, 1982, J. Neurosci., 2:1760-1774). In this study, we examined the time course of this process. Small, punctate acetylcholine receptor (AChR) clusters were detectable as early as 1.5 h after the addition of the beads. Subsequently, both the size and the number of the clusters increased with time until a saturation level was reached between 8-24 h. Because the onset and the site of the AChR clustering could be precisely marked, we were able to examine the early structural specializations associated with presumptive AChR clusters. At 1 h, when less than 20% bead-muscle contacts displayed AChR clusters, 70% of the contacts already exhibited a meshwork of 5-6-nm filaments, which were of the same size as the thin filaments within the myofibrils and thus may contain actin. A system of cisternae similar to the smooth endoplasmic reticulum was suspended within this meshwork, but other organelles were excluded from it. This meshwork, being the earliest cytoplasmic specialization at the presumptive AChR clusters and appearing before the clusters, may be a mechanism for the clustering process.

scholarly journals Agrin-induced acetylcholine receptor clustering in mammalian muscle requires tyrosine phosphorylation.

1996 ◽  
Vol 132 (5) ◽  
pp. 937-944 ◽  
Author(s):  
M Ferns ◽  
M Deiner ◽  
Z Hall
Keyword(s):  
Tyrosine Kinase ◽  
Tyrosine Phosphorylation ◽  
Tyrosine Kinase Inhibitors ◽  
Acetylcholine Receptor ◽  
Kinase Inhibitors ◽  
Beta Subunit ◽  
Experimental Conditions ◽  
Mammalian Muscle ◽  
Receptor Clusters ◽  
Achr Clustering

Agrin is thought to be the nerve-derived factor that initiates acetylcholine receptor (AChR) clustering at the developing neuromuscularjunction. We have investigated the signaling pathway in mouse C2 myotubes and report that agrin induces a rapid but transient tyrosine phosphorylation of the AChR beta subunit. As the beta-subunit tyrosine phosphorylation occurs before the formation of AChR clusters, it may serve as a precursor step in the clustering mechanism. Consistent with this, we observed that tyrosine phosphorylation of the beta subunit correlated precisely with the presence or absence of clustering under several experimental conditions. Moreover, two tyrosine kinase inhibitors, herbimycin and staurosporine, that blocked beta-subunit phosphorylation also blocked agrin-induced clustering. Surprisingly, the inhibitors also dispersed preformed AChR clusters, suggesting that the tyrosine phosphorylation of other proteins may be required for the maintenance of receptor clusters. These findings indicate that in mammalian muscle, agrin-induced AChR clustering occurs through a mechanism that requires tyrosine phosphorylation and may involve tyrosine phosphorylation of the AChR itself.

The role of lateral migration in the formation of acetylcholine receptor clusters induced by basic polypeptide-coated latex beads

1989 ◽  
Vol 131 (1) ◽  
pp. 197-206 ◽  
Author(s):  
H. Benjamin Peng ◽  
De-Yu Zhao ◽  
Ming-Zhi Xie ◽  
Ziwei Shen ◽  
Ken Jacobson
Keyword(s):  
Acetylcholine Receptor ◽  
Lateral Migration ◽  
Latex Beads ◽  
Receptor Clusters ◽  
Basic Polypeptide

scholarly journals Association of the postsynaptic 43K protein with newly formed acetylcholine receptor clusters in cultured muscle cells.

1985 ◽  
Vol 100 (5) ◽  
pp. 1698-1705 ◽  
Author(s):  
H B Peng ◽  
S C Froehner
Keyword(s):  
Acetylcholine Receptor ◽  
Binding Sites ◽  
Electric Organ ◽  
Muscle Cells ◽  
Postsynaptic Membrane ◽  
Latex Beads ◽  
Peripheral Membrane Protein ◽  
Double Label ◽  
Torpedo Electric Organ ◽  
Receptor Clusters

The postsynaptic membrane from Torpedo electric organ contains, in addition to the acetylcholine receptor (AChR), a major peripheral membrane protein of approximately 43,000 mol wt (43K protein). Previous studies have shown that this protein is closely associated with AChR and may be involved in anchoring receptors to the postsynaptic membrane. In this study, binding sites for monoclonal antibodies (mabs) to the 43K protein have been compared to the distribution of AChR in Xenopus laevis muscle cells in culture. In double label immunofluorescence experiments, clusters of AChR that occur spontaneously on these cells were stained with anti-43K mabs. Newly formed receptor clusters induced with positive polypeptide-coated latex beads were also stained with anti-43K mabs as early as 12 h after the application of the beads. Exact correspondence in the distribution of the anti-43K protein binding sites and the AChR was found in both types of clusters. These results suggest that the 43K protein becomes associated with AChR clusters during a period of active postsynaptic membrane differentiation. Thus, this protein may participate in the clustering process.

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

scholarly journals Stability of Fe-oxide nanoparticles coated with natural organic matter under relevant environmental conditions

2014 ◽  
Vol 70 (12) ◽  
pp. 2040-2046 ◽  
Author(s):  
L. Chekli ◽  
S. Phuntsho ◽  
L. D. Tijing ◽  
J. L. Zhou ◽  
J.-H. Kim ◽  
...  
Keyword(s):  
Organic Matter ◽  
Natural Organic Matter ◽  
Environmental Conditions ◽  
Divalent Cations ◽  
Oxide Nanoparticles ◽  
Fe Oxide ◽  
Coated Nanoparticles ◽  
Aggregation Behaviour ◽  
Physico Chemical ◽  
The Stability

Manufactured nanoparticles (MNPs) are increasingly released into the environment and thus research on their fate and behaviour in complex environmental samples is urgently needed. The fate of MNPs in the aquatic environment will mainly depend on the physico-chemical characteristics of the medium. The presence and concentration of natural organic matter (NOM) will play a significant role on the stability of MNPs by either decreasing or exacerbating the aggregation phenomenon. In this study, we firstly investigated the effect of NOM concentration on the aggregation behaviour of manufactured Fe-oxide nanoparticles. Then, the stability of the coated nanoparticles was assessed under relevant environmental conditions. Flow field-flow fractionation, an emerging method which is gaining popularity in the field of nanotechnology, has been employed and results have been compared to another size-measurement technique to provide increased confidence in the outcomes. Results showed enhanced stability when the nanoparticles are coated with NOM, which was due to electrosteric stabilisation. However, the presence of divalent cations, even at low concentration (i.e. less than 1 mM) was found to induce aggregation of NOM-coated nanoparticles via bridging mechanisms between NOM and Ca2+.

A novel AP180-related protein in vesicles that concentrate at acetylcholine receptor clusters

1998 ◽  
Vol 68 (4) ◽  
pp. 457-471 ◽  
Author(s):  
S. Bursztajn ◽  
S. Vincent ◽  
F.M. Brodsky ◽  
F. Benes ◽  
S.A. Morris
Keyword(s):  
Acetylcholine Receptor ◽  
Related Protein ◽  
Receptor Clusters

Measurement of Angular Acceleration of a Rigid Body Using Linear Accelerometers

1975 ◽  
Vol 42 (3) ◽  
pp. 552-556 ◽  
Author(s):  
A. J. Padgaonkar ◽  
K. W. Krieger ◽  
A. I. King
Keyword(s):  
Experimental Data ◽  
Rigid Body ◽  
Simple Procedure ◽  
Three Dimensional ◽  
Angular Acceleration ◽  
Theory And Practice ◽  
Body Segments ◽  
Impact Biomechanics ◽  
The Stability ◽  
Definition Of

The computation of angular acceleration of a rigid body from measured linear accelerations is a simple procedure, based on well-known kinematic principles. It can be shown that, in theory, a minimum of six linear accelerometers are required for a complete definition of the kinematics of a rigid body. However, recent attempts in impact biomechanics to determine general three-dimensional motion of body segments were unsuccessful when only six accelerometers were used. This paper demonstrates the cause for this inconsistency between theory and practice and specifies the conditions under which the method fails. In addition, an alternate method based on a special nine-accelerometer configuration is proposed. The stability and superiority of this approach are shown by the use of hypothetical as well as experimental data.

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