In myasthenia gravis (MG), specific antibodies directed against nicotinic acetylcholine receptor (nAChR) channels are produced. Recently, a distinct blockade of native embryonic-type nAChR channels by purified IgG from MG patients has been demonstrated. In the present study, we investigated the interaction of myasthenic IgG with recombinant embryonic- or adult-type nAChR channels expressed on human embryonic kidney (HEK) 293 cells. For the experiments, the patch clamp technique was applied in combination with an ultra-fast application system for agonists. Repetitive 20-ms pulses of 1 mM acetylcholine (ACh) were applied with or without purified IgG added to the perfusion system. The purified IgG from MG patients blocked currents through both, embryonic- and adult-type nAChR channels to a similar extent. A block by myasthenic IgG of adult-type nAChR channels, which are present exclusively at the postsynaptic membrane of the neuromuscular synapse, was shown to occur. The reversible pharmacological blockade of adult-type nAChR channels by myasthenic IgG may be one factor responsible for rapid fluctuations of weakness or rapid recovery of muscle strength after plasmapheresis in MG.
Copyright 2002 Wiley Periodicals, Inc.