Mechanism by which an elevation of extracellular glucide concentration induces pigment aggregation in medaka melanophores

Abstract

An increase in glucide concentration induces pigment aggregation in melanophores in the skin on scales isolated from the medaka, Oryzias latipes. In this study, hexoses (including the common D-isomers of glucose, galactose, fructose, and mannitol) were examined. Denervated melanophores were refractory to such stimuli. An α-adrenolytic agent, phentolamine, effectively blocked the responses of normally innervated melanophores. The pigment-aggregating action of glucide was inhibited by withdrawal of Ca2+ and Mg2+ ions from the medium. A specific blocker of voltage-dependent N-type Ca2+ channels, the ω-conotoxin GVIA, also inhibited the glucide action. The conclusion derived is that an elevation of glucide levels acts to open Ca2+ channels of presynaptic membranes of sympathetic postganglionic fibers, and the consequently released adrenergic transmitter acts on the effector cells to induce the aggregation of their pigmentary organelles. © 2002 Wiley-Liss, Inc.