Acetylcholine receptor (AChR) clusters of cultured rat myotubes, isolated by extraction with saponin (Bloch, R. J., 1984, J. Cell Biol. 99:984-993), contain a polypeptide that co-electrophoreses with purified muscle actins. A monoclonal antibody against actin reacts in immunoblots with this polypeptide and with purified actins. In indirect immunofluorescence, the antibody stains isolated AChR clusters only at AChR domains, strips of membrane within clusters that are rich in receptor. It also stains the postsynaptic region of the neuromuscular junction of adult rat skeletal muscle. Semiquantitative immunofluorescence analyses show that labeling by antiactin of isolated analyses show that labeling by antiactin of isolated AChR clusters is specific and saturable and that it varies linearly with the amount of AChR in the cluster. Filaments of purified gizzard myosin also bind preferentially at AChR-rich regions, and this binding is inhibited by MgATP. These experiments suggest that actin is ...
Overview on acetylcholine receptors pharmacology: differences between muscarinic and nicotinic receptors, classification, location, acetylcholine receptors and
Acetylcholine receptors (AChRs) are highly concentrated in the postsynaptic membrane at the neuromuscular junction. To investigate mechanisms that lead to the formation or maintenance of this synaptic specialization, we generated transgenic mice in which regulatory elements from the AChR alpha or epsilon-subunit genes are linked to a gene for a reporter protein that is targeted to the nucleus (nlacZ). Both transgenes were selectively expressed and developmentally regulated in muscle; nuclei in both extrafusal (ordinary) and intrafusal (spindle) muscle fibers were labeled. Within individual muscle fibers from epsilon-nlacZ mice, nuclei near synaptic sites were nlacZ-positive, whereas extrasynaptic nuclei were nlacZ-negative. In contrast, nlacZ was expressed in both synaptic and extrasynaptic nuclei when under the control of regulatory elements from the AChR alpha-subunit gene; however, synaptic nuclei were somewhat more intensely stained than extrasynaptic nuclei in a minority of muscle fibers ...
The possible role of nerve activity in triggering changes in the localization of acetylcholine receptors (AChRs) and cholinesterase (ChE) on nerve-contacted Xenopus muscle cells has been assessed. The localization of these molecules was examined on nerve-contacted and noncontacted muscle cells in cultures of spinal cord and myotomal muscle derived from Xenopus embryos. Sites of high AChR density were revealed by staining with fluorescent alpha-bungarotoxin and sites of ChE localization were revealed histochemically. Localization of AChRs and ChE at sites of nerve-muscle contact occurred when the culture medium contained 1.2 micron tetrodotoxin (TTX), 1.2 micron TTX, 10 mM magnesium, and no calcium salts, 1.2 micron TTX and 2 mM manganese, or 106 mM potassium methyl sulfate instead of sodium chloride. The nerve- contacted muscle cells in each of these modified culture media also exhibited a reduced incidence of AChR and ChE patches away from the site of contact. It is concluded that the neural ...
During neuromuscular junction formation ACh receptors accumulate at the nerve-contact region. It has been shown that this is at least partly due to lateral migration of existing receptors in the membrane (Anderson et al., 1977). Randomly diffusing ACh receptor molecules in the membrane may be trapped at the nerve-contact region to form a high receptor density area. If this were the major mechanism, cross-linking ACh receptors by tetravalent concanavalin A (Con A) should immobilize receptors and prevent nerve-induced receptor accumulation. We examined the effect of Con A on nerve-induced receptor accumulation and on the mobility of ACh receptors in cultured Xenopus muscle cells. ACh receptors were stained with tetramethyl rhodamine conjugated alpha- bungarotoxin. The cells were then treated briefly with Con A, and neural tube cells were added to these cultures. The mobility of ACh receptors was measured by the fluorescence photobleaching recovery method. The Con A treatment prevented rapid ...
A 125I-bungarotoxin labelling study of the acetylcholine receptor on the nerve-muscle junctions in the course of aging in the rat is reported. Attention is drawn to the fact that aging leads to an appreciable slowing down of the receptor degradation time, whereas no change occurs in its location.
Following the introduction by Neher and Sakmann (1976) of a voltage-clamp method for observing the currents flowing through single acetylcholine-receptor
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Cholinergic receptor information including symptoms, causes, diseases, symptoms, treatments, and other medical and health issues.
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