α‐Bungarotoxin Binding in House Fly Heads and Torpedo Electroplax

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Abstract
House fly heads contain a site that binds .alpha.-bungarotoxin with high affinity. It is present at .apprx. 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 site 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.