Electric organs are stacks of modified muscle cells, and each electrocyte face is essentially an enormous synapse. That concentrates acetylcholine receptors and the machinery of chemical transmission far beyond anything obtainable from ordinary muscle.
Working on Torpedo tissue with snake-venom toxins that bind the receptor tightly, researchers purified the nicotinic acetylcholine receptor in the early 1970s, then sequenced its subunits and later resolved its structure by electron microscopy of Torpedo membranes. Synaptic vesicles isolated from the same organ underpinned much of what is known about neurotransmitter release.
The rays involved were mainly Torpedo marmorata in Europe and Torpedo californica in North America. The result is that a receptor central to myasthenia gravis, to nerve agents and to nicotine addiction was first characterised not in a mammal but in a flat, slow, nocturnal fish that stuns its dinner.