Effect of passive transfer of myasthenic serum on mechanical, electrical and neuromuscular transmission properties of mouse skeletal muscle.

Neuromuscular transmission, muscle electrical activity and muscle mechanical properties have been studied in mice after the intraperitoneal transference of sera from myasthenic patients. Measurements of mepp's amplitude appear to be a suitable method for myasthenia gravis diagnosis since a high percentage of the sera from these patients caused a decrease in mepp's amplitude. The increase of the premenstrum weakness in myasthenic patients did not appear to be associated with greater fall of mepp's amplitude, since serum obtained in the premenstruum and far from it produced similar results. Myasthenic serum did not modify the electrical properties of innervated muscle sarcolemma. The resting membrane potential and the action potential parameters remained unchanged. However, tetrodotoxin resistant-action potentials of denervated muscles was reduced by myasthenic serum, possibly in association with receptor endocytosis process induced by the immunoglobulin. Muscle mechanical properties did not show alterations, even in the presence of positive titer of anti-striated muscle antibody.