Comparative analyses of the pigment-aggregating and -dispersing actions ofMCH on fish chromatophores

Citation
N. Oshima et al., Comparative analyses of the pigment-aggregating and -dispersing actions ofMCH on fish chromatophores, COMP BIOC C, 129(2), 2001, pp. 75-84
Citations number
35
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Pharmacology & Toxicology
Journal title
COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY C-TOXICOLOGY & PHARMACOLOGY
ISSN journal
1532-0456 → ACNP
Volume
129
Issue
2
Year of publication
2001
Pages
75 - 84
Database
ISI
SICI code
1532-0456(200106)129:2<75:CAOTPA>2.0.ZU;2-C
Abstract
In melanophores of the peppered catfish and the Nile tilapia, melanin-conce ntrating hormone (MCH) at low doses (< 1 muM) induced pigment aggregation, and the aggregated state was maintained in the presence of MCH. However, at higher MCH concentrations (such as I and 10 muM), pigment aggregation was immediately followed by some re-dispersion, even in the continued presence of MCH, which led to an apparent decrease in aggregation. This pigment-disp ersing activity at higher concentrations of MCH required extracellular Ca2 ions. By contrast, medaka melanophores responded to MCH only by pigment ag gregation, even at the highest concentration employed (10 muM). Since it is known that medaka melanophores possess specific receptors for cr-melanopho re-stimulating hormone (alpha -MSH), the possibility that interaction betwe en M:SH receptors and MCH at high doses in the presence of Ca2+ might cause pigment dispersion is ruled out. Cyclic MCH analogs, MCH (1-14) and MCH (5 -17), failed to induce pigment dispersion, whereas they induced aggregation of melanin granules. These results suggest that another type of MCH recept or that mediates pigment dispersion is present in catfish and tilapia melan ophores, and that intact MCH may be the only molecule that can bind to thes e receptors. Determinations of cAMP content in melanophores, which were iso lated from the skin of three fish species and treated with 10 nM or 10 muM MCH, indicate that MCH receptors mediating aggregation may be coupled with Gi protein, whereas MCH receptors that mediate dispersion may be linked to Gs. The response of erythrophores, xanthophores and leucophores to MCH at v arious concentrations was also examined, and the results suggest that the d istribution patterns of the two types of MCH receptors may differ among fis h species and among types of chromatophore in the same fish. (C) 2001 Elsev ier Science Inc. All rights reserved.