Journal of Neuroscience, Vol 4, 2297-2302, Copyright © 1984 by Society for Neuroscience
Neonatal denervation inhibits the normal postnatal decrease in endplate channel open time
SM Schuetze and S Vicini
The apparent mean channel open time (tau) of acetylcholine receptors (AChR)
at skeletal muscle endplates decreases greater than 3-fold during
development. In rat soleus muscles, the change occurs between postnatal
days 8 and 18 as channels with long apparent open times (tau = 4.5 msec)
disappear while channels with short apparent open times (tau = 1.5 msec)
increase in number. We studied the role of innervation in this process by
denervating neonatal soleus muscles prior to channel conversion. Tau at the
denervated endplates was assayed at various times between days 8 and 18 by
using fluctuation analysis. We found that early denervation blocked, or at
least delayed, channel conversion. Unexpectedly, there was enhanced
extrajunctional ACh sensitivity in the innervated muscles contralateral to
the denervated ones. This observation allowed us to compare the apparent
open times of junctional AChRs with those of extrajunctional AChRs 200
micron distant in the same innervated fibers. In developing muscles, tau at
the extrajunctional sites decreased in parallel with tau at the endplates.
Thus, neural regulation of AChR channel gating extends well beyond the
endplate boundaries.