The electroplaques of Astroscopus y-graecum were studied in situ with microelectrode recordings. Despite the distant taxonomic relations and the different origins of the organs, their properties in the teleost and torpedine marine electric fishes are remarkably similar. Only the innervated membrane (the dorsal) is electrogenically reactive in Astroscopus, and it, too, does not respond to electrical stimuli. As in the torpedine fishes, the uninnervated membrane of the eleetroplaques offers a very low resistance to the discharge of the innervated membrane. Additional direct evidence for electrical inexcitability of the reactive surface was obtained by denervating one of the bilateral organs. The denervated one did not respond to strong electrical stimuli which evoked responses in the opposite, innervated organ. The denervated electroplaques had a normal resting potential and were depolarized by acetylcholine and carbamylcholine similarly to normal cells. Other properties related to electrical inexcitability were also demonstrated. A pharmacological finding of considerable theoretical significance is that desensitization occurred on depolarizing ceils with acetylcholine but was absent on depolarizing them with carbamylcholine.
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