Acetylcholine receptors (AChRs) at innervated neuromuscular junctions are turned over at a far slower rate than the extrajunctional AChRs that appear along the muscle fiber after a period of denervation. We examined the effect of denervation on the degradation rate of junctional AChRs. Junctional AChRs were labeled in the mouse diaphram in vivo by injecting [125I]α-bungarotoxin into the thoracic cavity. Two days later one hemidiaphragm was denervated. The radioactivity remaining bound to the denervated and innervated hemidiaphragms was measured in groups of mice at intervals of 1 to 21 days after denervation. Between 4 and 8 days after denervation the rate of loss of radioactivity from the denervated hemidiaphragms increased from the control rate of 7% per day (half-life = 9.6 days) to 11% per day (half-life = 5.6 days). Radioactivity was lost from labeled extrajunctional receptors at a much faster rate, more than 50% per day (half-life = 22 h). Thus the degradation rate of preexisting junctional AChRs increased by about 40% after denervation, but remained far slower than the degradation rate of extrajunctional AChRs. Because some junctional AChRs labeled after denervation may have much faster turnover rates, this suggests that there are at least two different populations of AChRs at denervated neuromuscular junctions.
ASJC Scopus subject areas
- Developmental Neuroscience