ROLE OF CHOLINERGIC RECEPTORS IN MELANOPHORE RESPONSES OF AMPHIBIANS

Responses of isolated skin melanophores of Rang tigerina and Bufo mela nostictus to cholinergic drugs were studied using the Mean Melanophore Size Index assay to explore the nature and role of cellular receptors in melanophore regulation activity. Acetylcholine (Ach) in a concentr ation of 10(-7) to 6.4 x 10(-6) g/ml caused dispersion of the skin mel anophores of R. tigerina and B. melanostictus. These effects were bloc ked by both atropine and hyoscine in a concentration of 8 x 10(-6) g/m l each. Eserine augmented the melanophore dispersal effects of Ach. Th is potentiation of the dispersal effect of Ach by eserine was also ant agonised by hyoscine. Carbachol another specific cholinergic agonist s ignificantly caused dispersion of the melanophores of both the amphibi an species. She effects were also blocked by atropine and hyoscine. Th ese data indicate that cholinergic receptors of muscarinic type are pr esent an the melanophores of R. tigerina and B. melanostictus which me diate dispersion of integumental melanophores leading to darkening of the skin.