Prostanoids-induced dispersion in the melanophores of a carp Labeo rohita (Ham.).

Effects of three prostaglandins (i.e., prostanoids) and one of its precursors, arachidonic acid, were examined on the melanophores of the fish Labeo rohita (Ham.). PGE1, PGE2, PGF(2α) and arachidonic acid elicit a concentration-related dispersion in the fish melanophores. In vitro analysis of melanophores was performed through incubation of the isolated fish scales in different agonists and antagonists solutions. Dispersal effect of prostanoids may be mediated directly through the typical receptors or indirectly through release of neurotransmitter substance(s) from the melanophore nerve endings. Denervation of fish melanophores rendered them insensitive to prostanoid (PGF(2α)). Propranolol and verapamil completely inhibited the dispersal effects of PGF(2α); theophylline and indomethacine blocked the effects of higher concentrations of PGF(2α). During dispersing influence of PGF(2α), a free flux of Ca²âº ions was required and the indirectly released substance(s) from melanophore nerve endings would be the catecholamines of adrenergic and purinergic in nature.

Study of the effects of the casein derived bitter tastant on the melanophores in milieu with the melatonin receptors.

The present study was undertaken to ascertain whether the casein derived bitter tastant Cyclo (Leu-Trp) [CLT] has an affinity or not for the particular receptors of the pineal hormone, melatonin, on the melanophores of a major carp Labeo rohita (Ham.). The bitter tastant CLT, in the dose range of 3.34×10(-16) M to 3.34×10(-4) M, has induced an aggregatory effect but not in a dose dependent manner. Binding of CLT with the receptors may vary at different concentrations. Denervation of the melanophores has shown a complete inhibition of the CLT mediated aggregation. Prazosin has partially inhibited the aggregatory effect of CLT. Moreover, the bitter tastant's response is mediated through the α2 adrenoceptors only at particular dose ranges. The MT1 and MT2 melatonin receptor antagonist luzindole and the MT2 specific antagonist K185 have perfectly blocked the aggregatory effects of CLT. We have found that the CLT mediated aggregatory effect is dependent upon the release of neurotransmitters and the two subtypes of melatonin (MT) receptors (MT1 and MT2) possess a perfect affinity towards the bitter tastant CLT. Our study demands a need to further make a clinical research on the effects of bitter tastants on the physiology of the biological rhythm maintaining hormone melatonin.