The effects of myasthenic immunoglobulin G on neuromuscular transmission in mouse diaphragm

The effect of immunoglobulin G (IgG) from a patient with myasthenia gravis (MG) on neuromuscular transmission of an isolated mouse diaphragm preparation was studied by using electrophysiological methods. The frequency and amplitude of miniature endplate potentials (MEPPs) of the diaphragms obtained from mice injected intraperitoneally with purified IgG from MG patient were reduced by about 13% and 20%, respectively in comparison with results from normal mouse diaphragms. The amplitude of endplate potential (EPP) and the quantal content of EPPs were also reduced by about 21% and 7%, respectively. No significant changes in EPP and MEPP amplitudes were seen in the diaphragms of mice injected with normal IgG serum. It is postulated IgG from myasthenia gravis acts to interfere with both the receptor and the nerve terminal functions.