Pharmacological Profiles of the Subtypes of Muscarinic Cholinoceptors That Mediate Aggregation of Pigment in the Melanophores of Two Species of Catfish

Using selective antagonists, including pirenzepine, adiphenine, AF-DX116, gallamine, and 4-DAMP we attempted to characterize the muscarinic cholinoceptors on the melanophores of the translucent glass catfish Kryptopterus bicirrhis and the mailed catfish Corydoras paleatus. The M₃ receptor-selective antagonist, 4-DAMP, potently inhibited the acetylcholine-induced aggregation of pigment in both species. It appeared, therefore, that the receptors that mediated the cholinergically evoked aggregation of melanosomes in these species were of the M₃ muscarinic subtype.