Multiple molecular forms of acetylcholine receptors in cultured skeletal muscle cells: subcellular localization and...

Skeletal muscle cells of newborn rats, cultured in the absence of neuronal influence, were found to contain two types of cell surface acetylcholine receptors as demonstrated by isoelectric focusing. The isoelectric points of the two types of receptors were indistinguishable from those of junctional and extrajunctional types of receptors in mature animals. The cultured cells had two classes of intracellular alpha-bungarotoxin (alpha BT) binding components; one had the same sedimentation coefficient as that of surface receptors (9S), and the other had much smaller apparent molecular weights. Only a single major component was detected by isoelectric focusing analysis of the 9S intracellular alpha BT binding component, with a pI value close to that of the extrajunctional receptor. These results suggest that the junctional and extrajunctional types of receptors may be synthesized through a common precursor.