Alpha-bungarotoxin binding in house fly heads and Torpedo electroplax

House fly heads contain a site that binds alpha-bungarotoxin with high affinity. It is present at about 23 pmol/g of heads and binds alpha-bungarotoxin (labeled with [3H]pyridoxamine phosphate) reversibly with a Kd of 6 nM. The effects of 48 drugs have been compared on the alpha-bungarotoxin binding sites of house fly and Torpedo. The pharmacology of the house fly sites is similar to that previously reported for neuronal alpha-bungarotoxin binding sites in both vertebrates and invertebrates and is distinguishable from that of the classic nicotinic neuromuscular acetylcholine receptor, as exemplified by that of Torpedo electroplax. Differences between the house fly site and Torpedo include higher affinities of the Torpedo receptor for decamethonium, hexamethonium, carbamylcholine, and acetyl-beta-methylcholine, but lower affinities for nicotine, atropine, and dihydro-beta-erythroidine.