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Coated and smooth vesicles participate in acetylcholine receptor transport
Authors:Dr Sherry Bursztajn  Harvey B Nudleman  Stephen A Berman
Institution:(1) Departments of Neurology and Cell Biology, Baylor College of Medicine, Houston, Texas, USA;(2) Department of Neurology, University of Chicago, Chicago, Illinois, USA;(3) Department of Neurology, Texas Medical Center, Baylor College of Medicine, 77030 Houston, Texas, USA
Abstract:Summary The removal of the acetylcholine receptors (AChRs) from the surface of muscle cells serves as an important mechanism in the regulation of the AChR turnover rate. Our previous studies have shown that cultured myotubes contain coated pits and vesicles bearing agr-bungarotoxin (agrBTX)-binding sites (Bursztajn 1984; Bursztajn and Fischbach 1984). In this study we have used agrBTX conjugated to horseradish peroxidase (HRP) and quantitative electron microscopy to determine the intracellular pathway(s) of acetylcholine receptors during the internalization process. To accomplish this, cultured rat myotubes were incubated with agrBTX-HRP at 4° C after which cells were washed and incubated at 37° C for 0 min to 2 h. After warming the cells, coated pits, coated vesicles and smooth membraned vesicles containing the peroxidase reaction product were present. A threefold increase in coated vesicles containing the reaction product was observed 1 min after warming the cells. The number of smooth-membraned vesicles remained constant at this time point. However, 5 to 15 min after warming the cells, a fivefold increase in the number of smooth membraned vesicles was observed. After 1 h at 37° C the reaction product was present in the lysosomal like bodies, but was not observed in the Golgi complex or the small coated vesicles associated with the Golgi complex. Our observations indicate that there is a size segregation between those coated vesicles containing agrBTX-HRP reaction product and those in which reaction product is absent. Our studies also suggest that within minutes of AChR internalization coated vesicles lose their coat and become smooth-membraned vesicles.
Keywords:ACh receptor  Coated vesicles  Endocytosis  agrBTX" target="_blank">gif" alt="agr" align="BASELINE" BORDER="0">BTX  Cultured myotubes
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