Detection of nicotinic cholinergic transmission in [formula omitted][formula omitted] electrop lax

Abstract

Biochemical and electrophysiological studies were conducted on the electric organ of the electric fish of the Nile, Malapterurus electricus , in order to determine if transmission was chemically mediated. There was no binding of [ 3H] acetylcholine, [ 3H] quinuclidinyl benzilate or [ 3H]-perhydrohistrionicotoxin; but low acetylcholinesterase activity was observed, as was binding of [ 125I] α-bungarotoxin. The latter binding was detectable at 0.85 ± 0.07 pmol/g tissue, and was totally inhibited by 1 μM α-bungarotoxin or 100 μM d-tubocurarine. A tetrodotoxin-sensitive action potential was measured which was Na +- dependent. Depolarization (30–40 mV) was caused by carbamylcholine, and this was blocked by d-tubocurarine or α-bungarotoxin. The data suggest that this electric organ which may be a rich source for electrically excitable channels, is innervated by nicotonic cholinergic motoneurons, but the concentrations of acetylcholine receptors and acetylcholinesterase are very low.