A study on melanophore receptors of Papiliochromis ramirezi (Teleostei, Cichlidae)

Melanophores of Papiliochromis ramirezi aggregate their melanosomes in the presence of catecholamines. Their order of potency are: at 10(-4) M, norepinephrine greater than isoproterenol = epinephrine; at 10(-6) and 10(-8) M, norepinephrine = isoproterenol greater than epinephrine. These effects are antagonized not only by phentolamine but also by propranolol. The catecholamines are unable to induce pigment dispersion. Melanosome dispersion is obtained with cholinergic drugs and the order of potency is nicotine greater than acetylcholine = pilocarpine. Their effects are inhibited by atropine and also by d-tubocurarine and potentiated by physostigmine. The evidences suggest the presence of undifferentiated adrenoceptors, related to the melanosome aggregation and undifferentiated cholinoceptors related to the melanosome dispersion.