In vitro responses of fish melanophores to lyophilized extracts of Psoralea corylifolia seeds and pure psoralen

Objective: The present work was carried out to determine the effects of lyophilized seed extracts of P. corylifolia, along with pure psoralen on the isolated scale melanophores of Channa punctatus Bloch. (Channidae), which are a disguised type of smooth muscle cells and offer excellent in vitro opportunities for studying the effects of drugs. Materials and methods: Effects of lyophilized extracts of P. corylifolia and pure psoralen were studied on the isolated scale melanophores of C. punctatus as per the modified method of Bhattacharya et al. (1976). Results: The lyophilized extract of P. corylifolia and its active ingredient psoralen caused significant melanin dispersal responses leading to darkening of the fish scale melanophores, which were completely antagonized by atropine and hyoscine. These melanin dispersal effects were also found to be markedly potentiated by neostigmine, an anticholinesterase agent. Discussion: In the present study, the lyophilized extract of P. corylifolia seeds and standard psoralen in different dose ranges induced powerful melanin dispersal effects of the previously adrenaline-aggregated isolated scale melanophores of C. punctatus. Comparatively, psoralen caused a more sustained and powerful melanin dispersal within the isolated fish melanophores and interestingly the concentrations required to achieve maximal dispersion of melanophore were 10 times less than that of lyophilized seed extract of P. corylifolia. The physiologically significant dose-related melanin dispersion effects of lyophilized P. corylifolia seeds and synthetic psoralen per se were found to be completely abolished by atropine and hyoscine, which are specific cholino-muscarinic receptor blockers. These data strongly indicate that in the fish C. punctatus, the dispersion of melanin granules within the scale melanophores is mediated by choline receptors of muscarinic nature. Conclusion: It appears that the melanin dispersal effects of the extracts of P. corylifolia and pure psoralen leading to skin darkening are mediated by cholino-muscarinic- or cholino-psoralen-like receptors having similar properties.