Postsynaptic distribution of acetylcholine receptors in electroplax of the torpedine ray, Narcine brasiliensis.

Other investigations have shown that many postsynaptic membranes which contain high densities of the nicotinic acetylcholine receptor appear to be unusually thick in electron micrographs. This peculiarity is believed to arise in part from the receptor protein itself. We show that in electroplax of Narcine brasiliensis, the thick membrane is found in juxtaneural postsynaptic regions, but not in deeper portions of junctional fold-like postsynaptic papillae or in extrasynaptic regions of the innervated face. Autoradiographic localization of receptor-bound [125I]alpha-bungarotoxin confirms that high densities of receptor are confined to juxtaneural regions. Narcine electric tissue thus provides a system for biochemical study of an acetylcholine receptor localization similar to that found at the mammalian or amphibian neuromuscular junction. Limited data suggest that similar postsynaptic distributions of receptor also occur in electroplax of several species of Torpedo.