title: A new in vitro melanophore bioassay for MSH using tail-fins of Xenopus tadpoles.
abstract: A new in vitro melanophore system is described, which employs pieces from the ventral tail-fin of Xenopus laevis tadpoles. Tail-fin melanophores in vitro retain the ability to disperse their pigment in darkness and to reaggregate it upon illumination. In the light, alpha-MSH, cAMP, dibutyryl-cAMP and theophylline induce a concentration-dependent pigment dispersion. The log dose-response curve obtained with alpha-MSH is sigmoidal with a linear portion between 0.5 and 2.0 ng alpha-MSH/ml. In this range, the log dose-response curve can be used as the standard curve in a bioassay for melanotropic activity, applying either the melanophore index (assay I) or a photometric transmittance measurement (assay II) for the quantification of the melanophore response. To prevent interference from the light/darkness response, light of 400-500 nm (to which the melanophores are most sensitive) was used during the assay. Both assays show high precision (lambda I = 0.13, lambda II = 0.11). Several peptides derived from alpha-MSH were tested for their melanotropic activity. The in vitro Xenopus melanophore system offers unique properties for the study of alpha-MSH action: (1) the melanophore system is uncontaminated with other chromatophores; (2) to date it is the only system suitable for photoaffinity labelling of alpha-MSH receptors; and (3) the melanophore receptor requirements differ from those of Rana.
mesh_terms: D000818:Animals; D001681:Biological Assay / Q000379:methods*; D002449:Cell Aggregation; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D007814:Larva; D008027:Light; D009074:Melanocyte-Stimulating Hormones / Q000032:analysis / Q000494:pharmacology*; D008547:Melanophores / Q000187:drug effects*; D013329:Structure-Activity Relationship; D013623:Tail; D014982:Xenopus laevis
chemical_list: D009074:Melanocyte-Stimulating Hormones