scholarly journals Metabolic stabilization of acetylcholine receptors in vertebrate neuromuscular junction by muscle activity.

1990 ◽  
Vol 111 (2) ◽  
pp. 655-661 ◽  
Author(s):  
S Rotzler ◽  
H R Brenner
Keyword(s):  
Skeletal Muscle ◽  
Neuromuscular Junction ◽  
Muscle Activity ◽  
Acetylcholine Receptors ◽  
Muscle Stimulation ◽  
Cluster Growth ◽  
Rat Skeletal Muscle ◽  
Achr Cluster ◽  
End Plate ◽  
Alpha Bungarotoxin

The effects of muscle activity on the growth of synaptic acetylcholine receptor (AChR) accumulations and on the metabolic AChR stability were investigated in rat skeletal muscle. Ectopic end plates induced surgically in adult soleus muscle were denervated early during development when junctional AChR number and stability were still low and, subsequently, muscles were either left inactive or they were kept active by chronic exogenous stimulation. AChR numbers per ectopic AChR cluster and AChR stabilities were estimated from the radioactivity and its decay with time, respectively, of end plate sites whose AChRs had been labeled with 125I-alpha-bungarotoxin (alpha-butx). The results show that the metabolic stability of the AChRs in ectopic clusters is reversibly increased by muscle activity even when innervation is eliminated very early in development. 1 d of stimulation is sufficient to stabilize the AChRs in ectopic AChR clusters. Muscle stimulation also produced an increase in the number of AChRs at early denervated end plates. Activity-induced cluster growth occurs mainly by an increase in area rather than in AChR density, and for at least 10 d after denervation is comparable to that in normally developing ectopic end plates. The possible involvement of AChR stabilization in end plate growth is discussed.

scholarly journals Effect of agrin on the distribution of acetylcholine receptors and sodium channels on adult skeletal muscle fibers in culture.

1991 ◽  
Vol 115 (3) ◽  
pp. 765-778 ◽  
Author(s):  
M T Lupa ◽  
J H Caldwell
Keyword(s):  
Skeletal Muscle ◽  
Acetylcholine Receptors ◽  
Muscle Fibers ◽  
Postsynaptic Membrane ◽  
Na Channel ◽  
High Concentration ◽  
Achr Cluster ◽  
Adult Skeletal Muscle ◽  
Skeletal Muscle Fibers ◽  
Alpha Bungarotoxin

We used the loose patch voltage clamp technique and rhodamine-conjugated alpha-bungarotoxin to study the regulation of Na channel (NaCh) and acetylcholine receptor (AChR) distribution on dissociated adult skeletal muscle fibers in culture. The aggregate of AChRs and NaChs normally found in the postsynaptic membrane of these cells gradually fragmented and dispersed from the synaptic region after several days in culture. This dispersal was the result of the collagenase treatment used to dissociate the cells, suggesting that a factor associated with the extracellular matrix was responsible for maintaining the high concentration of AchRs and NaChs at the neuromuscular junction. We tested whether the basal lamina protein agrin, which has been shown to induce the aggregation of AChRs on embryonic myotubes, could similarly influence the distribution of NaChs. By following identified fibers, we found that agrin accelerated both the fragmentation of the endplate AChR cluster into smaller patches as well as the appearance of new AChR clusters away from the endplate. AChR patches which were fragments of the original endplate retained a high density of NaChs, but no new NaCh hotspots were found elsewhere on the fiber, including sites of newly formed AChR clusters. The results are consistent with the hypothesis that extracellular signals regulate the distribution of AChRs and NaChs on skeletal muscle fibers. While agrin probably serves this function for the AChR, it does not appear to play a role in the regulation of the NaCh distribution.

Trophic effect of iron-bound transferrin on acetylcholine receptors in rat skeletal muscle in vivo

1983 ◽  
Vol 38 (3) ◽  
pp. 303-307 ◽  
Author(s):  
Keiji Wada ◽  
Satoshi Ueno ◽  
Takanori Hazama ◽  
Hiro-O Yoshikawa ◽  
Saburo Ogasahara ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Acetylcholine Receptors ◽  
Rat Skeletal Muscle ◽  
Trophic Effect

scholarly journals In vivo recovery of muscle contraction after alpha-bungarotoxin binding.

1975 ◽  
Vol 66 (1) ◽  
pp. 209-213 ◽  
Author(s):  
H C Fertuck ◽  
W Woodward ◽  
M M Salpeter
Keyword(s):  
Fine Structure ◽  
Neuromuscular Junction ◽  
Muscle Contraction ◽  
Acetylcholine Receptors ◽  
Actinomycin D ◽  
Recovery Period ◽  
Em Autoradiography ◽  
Alpha Bungarotoxin ◽  
In Vivo Recovery

Acetylcholine receptors were inactivated in vivo at the mouse neuromuscular junction using alpha-bungarotoxin (alpha-BTX). It was found that neurally produced muscle contraction recovered within 4-8 days (halftime similar to 3 days). Actinomycin D interfered with this recovery, but did not affect normal nerve-stimulated muscle contraction. If the response was initially eliminated by [125-I]alpha-BTX and the end plates examined by EM autoradiography, no evidence of mass internalization of bound radioactivity during recovery was seen. The fine structure of the end plates and muscle was unaltered during the post-alpha-BTX recovery period.

scholarly journals Interaction of di-iodinated 125I-labelled α-bungarotoxin and reversible cholinergic ligands with intact synaptic acetylcholine receptors on isolated skeletal-muscle fibres from the rat

1979 ◽  
Vol 181 (3) ◽  
pp. 545-557 ◽  
Author(s):  
P Darveniza ◽  
J A Morgan-Hughes ◽  
E J Thompson
Keyword(s):  
Skeletal Muscle ◽  
Dissociation Constant ◽  
Binding Sites ◽  
Acetylcholine Receptors ◽  
Time Course ◽  
Muscle Fibres ◽  
First Order ◽  
Toxin Binding ◽  
Alpha Bungarotoxin ◽  
Skeletal Muscle Fibres

1. Intact synaptic acetylcholine receptors on freshly isolated rat skeletal-muscle fibres were characterized by their interaction with di-iodinated 125I-labelled alpha-bungarotoxin, acetylcholine and other cholinergic ligands at room temperature (22 deggrees C). 2. The time course and concentration dependence of 125I-labelled alpha-bungarotoxin association conformed to a bimolecular mechanism. In time-course experiments with different concentrations of 125I-labelled alpha-bungarotoxin (1.4–200 nM) the bimolecular-association rate constant, k + 1, was (2.27 +/- 0.49) × 10(4)M-1.S-1 (mean +/- S.D., N = 10). In concentration-dependence experiments, k + 1 was 2.10 × 10(4)M-1.S-1 and 1.74 × 10(4) M-1.S-1 with 10 and 135 min incubations respectively. In association experiments the first-order rate constant was proportional to the 125I-labelled alpha-bungarotoxin concentration. 125I-Labelled alpha-bungarotoxin dissociation was first order with a dissociation constant, k-1, less than or equal to 3 × 10(-6)S(-1) (half-life greater than or equal to 60 h.) The results indicated a single class of high-affinity toxin-binding sites at the end-plate with an equilibrium dissociation constant, Kd, equal to or less than 100 pM. The number of toxin-binding sites was (3.62 +/- 0.46) × 10(7) (mean +/- S.D., n = 22) per rat end-plate. 3. The apparent inhibitor dissociation constants, Ki, for reversible cholinergic ligands were determined by studying their effect at equilibrium on the rate of 125I-labelled alpha-bungarotoxin binding. There was heterogeneity of binding sites for cholinergic ligands, which were independent and non-interacting with antagonists. In contrast agonist affinity decreased with increasing receptor occupancy. Cholinergic ligands in excess inhibited over 90% of 125I-labelled alpha-bungarotoxin binding. 4. Cholinergic ligand binding was accompanied by an increase in entropy, which was greater for the agonist carbachol (delta So = +0.46 kJ.mol-1.K-1) than the antagonist tubocurarine (delta So = +0.26 kJ.mol-1.K-1). 5. The entropy and affinity changes that accompanied agonist binding suggested that agonists induced significant conformational changes in intact acetylcholine receptors. 6. The affinity and specificity of 125I-labelled alpha-bungarotoxin and tubocurarine binding to synaptic acetylcholine receptors from slow and fast muscle fibres were the same. 7. The study of binding only requires milligram amounts of tissue and may have application to other neurobiological studies and to the study of human neuromuscular disorders.

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