JBC, Vol. 254, Issue 13, 5652-5657, Jul, 1979
Concanavalin A inhibition of alpha-bungarotoxin binding to a nonfusing muscle cell line
J. Boulter and J. Patrick
Incubation of a nonfusing muscle cell line, BC3H1, with concanavalin A (Con
A) results in a maximum decrease of 35% in the cell's ability to bind
alpha-bungarotoxin (alpha-BuTx). The Con A-induced inhibition of
125I-alpha-BuTx binding is reversible and the degree of inhibition
parallels the degree of saturation of Con A binding sites on the cell
surface. The maximum level of Con A-induced inhibition of 125I-alpha-BuTx
binding is not affected by increasing the time of incubation in Con A,
using higher concentrations of Con A or by increasing the time of
incubation in the presence of 125I-alpha-BuTx. In addition, all BC3H1 cells
in culture are sensitive to the Con A-induced inhibition of 125I-alpha-BuTx
binding. A comparison of the pseudo-first order rate constants for
125I-alpha-BuTx binding to untreated (8.6 x 10(4) M-1 S-1) and Con
A-treated (5.4 x 10(4) M-1 S-1) BC3H1 cells, however, shows that those
acetylcholine receptors in Con A-treated cells which bind 125I-alpha-BuTx
do so with a lowered apparent affinity. Partial inhibition of toxin-binding
capacity is not a consequence of two classes of acetylcholine receptors on
the cell surface. Furthermore, individual receptors experience partial
inhibition of their binding capacity by Con A, resulting in receptors with
at least one binding site blocked and at least one site available for
alpha-BuTx binding.
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