Expression of acetylcholine receptor isoforms at extraocular muscle endplates.

PURPOSE To determine the expression of fetal and adult acetylcholine receptor (AChR) isoforms among extraocular muscle (EOM) en plaque and en grappe endplates. METHODS Antibodies against peptide fragments of the gamma- and epsilon-subunits of the fetal and adult AChRs and alpha-bungarotoxin were used in immunofluorescence experiments to stain rat neonatal leg, adult diaphragm, and extraocular rectus muscle endplates. RESULTS Anti-epsilon antibodies intensely stained diaphragm endplates weakly stained rare neonatal endplates. Anti-gamma antibodies stained neonatal, but not diaphragm, endplates. Anti-epsilon antibodies bound to all en plaque and en grappe endplates of extraocular muscle. Anti-gamma antibodies bound to global and orbital en grappe endplates. All en plaque endplates of the orbital region and a subset of endplates in the global region stained with anti-gamma antibodies. CONCLUSIONS All en grappe endplates and certain en plaque endplates of EOM are the only mature endplates that coexpress the adult and fetal AChR isoforms. The expression of both isoforms may be important to determine contractile properties, protein expression regulation, and EOM susceptibility to myasthenia gravis.