Journal of Neuroscience, Vol 6, 581-589, Copyright © 1986 by Society for Neuroscience
Elimination of preexistent acetylcholine receptor clusters induced by the formation of new clusters in the absence of nerve
HB Peng
Acetylcholine receptors (AChRs) form clusters spontaneously in cultured
Xenopus myotomal muscle cells in the absence of innervation. Innervation
causes a dispersal of these clusters, as well as the formation of new
clusters along the neuromuscular contact. To examine whether this dispersal
process is dependent upon the presence of the nerve or can be effected by
the formation of new clusters alone, we examined the stability of the
preexistent clusters during the formation of new AChR clusters induced by
basic polypeptide-coated latex beads. These beads cause a rapid development
of clusters in cultured Xenopus muscle cells, and the size and the number
of clusters can be experimentally manipulated by varying the size and
number of beads applied to the culture. Accompanying the bead-induced
formation of new clusters was an observed suppression of preexistent
clusters, as shown by fluorescence microscopy after staining with
rhodamine-conjugated alpha-bungarotoxin. This process of extra-bead cluster
removal can be speeded up by treating the cultures with more beads or using
beads of larger diameter. Furthermore, if the beads are applied before the
spontaneous AChR clustering, no extra-bead clusters are formed. Thus, the
latex beads can mimic the nerve in both causing the formation of new
clusters and the dispersal of preexistent clusters. Although the receptor
clusters are dispersed by the beads, the density of diffuse receptors, as
shown by autoradiography with 125I-conjugated alpha- bungarotoxin does not
decrease in the short-term cultures under study. This indicates that the
dispersal of preexistent clusters is not due to a depletion of the surface
pool of AChRs.(ABSTRACT TRUNCATED AT 250 WORDS)