An endogenous 5‐HT₇ receptor mediates pigment granule dispersion in Xenopus laevis melanophores

Abstract

1 Melatonin (5-methoxy N-acetyltryptamine) and serotonin (5-HT) exert rapid, but opposite eects on pigment granule distribution in Xenopus laevis melanophores. Low concentrations of melatonin (10 711 ± 10 79 M) cause a dramatic perinuclear aggregation of the melanin-containing granules, while 5-HT (10 78 ± 10 75 M) disperses pigment granules throughout the cell. 2 The present study found that pharmacological doses of melatonin (510 76 M) induced a timeand concentration-dependent pigment granule dispersion, which was mediated by an endogenous melanophore 5-HT receptor. (54)] was also consistent with an action on 5-HT 7 receptors. 5 RT ± PCR con®rmed that melanophores express 5-HT 7 receptor mRNA. The pigment dispersing eect of high melatonin concentrations in melanophores is most likely mediated by activation of 5-HT 7 receptors. Conceivably some of the eects attributed to pharmacological doses of melatonin in mammals may be mediated by activation of 5-HT 7 receptors.

Acute sleep‐promoting action of the melatonin agonist, ramelteon, in the rat

“…2A) with ramelteon approximately tenfold more potent (ramelteon pEC 50 11.48, melatonin pEC 50 10.41). Previously, high concentrations (>1 μ m ) of melatonin have been shown to activate a melanophore 5‐HT 7 receptor which triggers the dispersion of pigment granules in these cells [21]. The ability of ramelteon to activate this 5‐HT 7 receptor was tested (Fig.…”

Cloning and expression of a zebrafish 5-HT2C receptor gene

“…The role of 5-HT in these tissues of zebrafish is unknown. In mammals, 5-HT has physiological and developmental functions in the cardiovascular system, but these actions are mediated by 5-HT 1B , 5-HT 2A , 5-HT 2B , 5-HT 4 , and 5-HT 7 and not by 5-HT 2C receptors, although the expression of the 5-HT2C receptor has been detected in these tissues (Asada et al, 2009;Dube and Amireault, 2007;Glusa and Pertz, 2000;Ishida, 1999;Kaumann and Levy, 2006;Ontsouka, 2004;Teh and Sugden, 2001;Villalon and Centurion, 2007;Westbroek, 2001). A function of 5-HT in the regulation of oocyte development has been demonstrated in Fundulus heteroclitus (Cerda et al, 1998).…”

Vertebrate melanophores as potential model for drug discovery and development: A review

“…In amphibians such as Xenopus laevis, a very low concentration of melatonin activates the Mel (1c) receptor subtype triggering granule aggregation and lightening of skin color. It was also reported that melatonin exerts rapid effects on pigment granule distribution in Xenopus laevis melanophores [115]. Low concentrations of melatonin (10 -11 to 10 -9 M) cause a dramatic perinuclear aggregation of the melanin-containing granules [115].…”

“…It was also reported that melatonin exerts rapid effects on pigment granule distribution in Xenopus laevis melanophores [115]. Low concentrations of melatonin (10 -11 to 10 -9 M) cause a dramatic perinuclear aggregation of the melanin-containing granules [115]. Additionally, Mel (1c) receptor activation reduces intracellular cAMP via a pertussis toxin-sensitive inhibitory G-protein (Gi), but how this and other intracellular signals regulate pigment movement is not yet fully understood [116].…”

“…Serotonin increased the intracellular levels of cAMP and induced pigment dispersion in the cells. Furthermore, Teh and Sudgen [115] reported the involvement of an endogenous 5-HT7 receptor in pigment granule dispersion in Xenopus laevis melanophores. 5-HT produced a concentration-dependent elevation of melanophore cyclic AMP, and 5-HT-induced dispersion was blocked by H89 (10(-4) M), an inhibitor of protein kinase A (PKA), but not by a PKC inhibitor (Ro 31-8220, 10(-5) M), indicating a vital role for cyclic AMP in 5-HT-induced dispersion.…”