Effect of acetylcholine on melanophores of Rana tigrina

Acetylcholine produced melanin aggregation and blanching of skin colour in Rana tigrina, the common Indian frog. The effects were more prolonged in frogs pretreated with an anticholinesterase agent. Acetylcholine effects were not antagonized by either m-cholinolytic (atropine) or n-cholinolytic (pentolinium) agents, but were markedly inhibited by procaine. The results have been discussed in the light of the well-known membrane-stabilizing effect of procaine.