Species differences determine azido phencyclidine labeling pattern in desensitized nicotinic acetylcholine receptors

Acetylcholine receptor enriched membranes from Torpedo ocellata, Torpedo marmorata and Torpedo californica were studied using [³H] azido-phencyclidine (AZ-PCP). [³H]-PCP binding to receptors from all three species revealed marked similarities. Photoaffinity labeling by [³H]-AZ-PCP resulted in the tagging of mainly α, β and δ subunits in all species. When carbamylcholine was added, it enhanced the labeling of β subunits in T. ocellata, δ in T. marmorata and α in T. californica, suggesting species differences in the photolabeling pattern. Multiple homologous binding sites for PCP between the receptor subunits would allow small variations in receptor structure to be manifested in labeling by AZ-PCP, with no differences in binding and functional properties of the receptors.