| Abstract: | 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. |
