Studies on the Ability of Acetylcholine Receptors to Bind Alpha‐bungarotoxin After Exposure to Myasthenic Serum*

The purpose of the present experiment was to determine if there is a factor in serum of patients with myasthenia gravis (MG) that interferes with binding of (125I)-alpha-bungarotoxin to acetylcholine receptors of normal mouse diaphragm. Diaphragms were incubated aerobically for 1 hour in either Krebs-Henseleit solution, MG serum, or control serum, and then (125I)-alpha bungarotoxin was added for 2 further hours at a concentration of 1 mug/ml. After 12 rinses in Krebs-Henseleit solution for another hour, radioactivity was counted. Binding after exposure to MG serum was compared to that obtained after exposure to Krebs-Henseleit solution or control serum. Sixteen sera from 14 controls, 18 sera from 15 patients with moderate generalized MG, and seven sera from seven patients on alternate-day prednisone therapy (six with severe generalized MG, one with myasthenic syndrome) were tested by this method. No significant difference in alpha-bungarotoxin binding was observed between normal mouse diaphragm incubated in MG sera and those incubated in control sera.