Content of acetylcholine receptor and antibodies bound to receptor in myasthenia gravis, experimental autoimmune myasthenia gravis, and Eaton‐Lambert syndrome

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Abstract
The acetylcholine receptor content of intercostal muscle biopsies from patients with myasthenia gravis is reduced, and many of the remaining receptors have antibodies bound to them. Decreased receptor content and inhibition of receptor activity by bound antibodies can account for the reduced amplitude of the miniature endplate potential in these patients. Patients with Eaton-Lambert syndrome, who release reduced numbers of acetylcholine quanta, have normal receptor content and miniature endplate potential amplitude, and do not have antibodies bound to their receptors. As the severity of myasthenia gravis increases, the content of receptor remaining unbound by antibody decreases, as does miniature endplate potential amplitude. Similar decreases in receptor content and similar concentrations of antibody-labeled receptor are found in rats with experimental autoimmune myasthenia gravis. Regardless of the severity of their myasthenia, receptor content in rats does not decrease much below 40 percent of normal, and increasing weakness is associated with the binding of antibodies to an increasing fraction of the remaining receptors. In both myasthenia gravis and its animal model, a decrease in the content of fully active receptor is probably the most important factor impairing neuromuscular transmission. Pathologic mechanisms responsible for decreased receptor content and alteration of postsynaptic membrane morphology are discussed.

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