Journal of Neuroscience, Vol 6, 1941-1951, Copyright © 1986 by Society for Neuroscience
Concanavalin A prevents acetylcholine receptor redistribution in Xenopus nerve-muscle cultures
Y Kidokoro, B Brass and H Kuromi
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 diffusion of ACh
receptors as well as nerve-induced receptor accumulation. Functional
synapse formation was not inhibited by this treatment. In contrast,
divalent succinyl Con A did not affect the mobility of ACh receptors nor
prevent nerve-induced ACh receptor accumulation. When the Con A
concentration was varied, the blocking effect on the nerve-induced receptor
accumulation changed in parallel with the mobile fraction of receptors.
Newly inserted ACh receptors after the Con A treatment were found to be
mobile and to accumulate at the nerve-contact region. In these cultures,
new receptors accumulated around old, immobilized receptors in some areas
along the nerve contact. This observation suggests that new receptors were
inserted elsewhere and migrated to the nerve-contact region surrounding
immobilized old ones. In addition to the accumulation of receptors, the
nerve disperses preexisting receptor clusters prior to induction of
high-density regions along the contact area, and, at this early stage,
denervation disperses nerve-induced receptor clusters in Xenopus cultures
(Kuromi and Kidokoro, 1984a, b). When cultures were treated with Con A,
neither of these events occurred, suggesting that these are also
diffusion-mediated.