The developmental change in immunological properties of the acetylcholine receptor in rat muscle

We have used serum from a patient with myasthenia gravis containing antibodies that recognize unique determinants on the extrajunctional acetylcholine receptor (AChR) to characterize the AChR in extracts of developing rat muscle. Using mixtures of extrajunctional and junctional AChR from denervated and normal adult muscle, respectively, as standards, we estimated the proportion of each receptor type in muscle extracts of embryonic and neonatal rats. The presence of the immunologically adult form of the AChR was first detected during the first postnatal week. Analysis by two methods showed that this is also the time during which the proportion of the total muscle receptor that is at end plates increases.