LEUCOPHORES OF THE DARK-BANDED ROCKFISH SEBASTES INERMIS .1. ADRENERGIC-MECHANISMS THAT CONTROL THE MOVEMENTS OF PIGMENT

There are unusual chromatophores, which appear yellowish in reflected light, in the integument of the dark-banded rockfish Sebastes inermis. Earlier ultrastructural observations revealed that these chromatophor es are leucophores with granular pigment organelles [13]. In the prese nt experiments, adrenergic mechanisms controlling the migration of pig ment associated with these chromatophores were investigated. K+ ions i nduced dispersion of the pigment. The dispersion was prevented by prop ranolol, an adrenergic blocker, and was absent from denervated prepara tions, suggesting that the chromatophores are innervated by adrenergic nerves. Adrenergic agonists, namely, isoproterenol and norepinephrine but not epinephrine, induced the dispersion of pigment. Propranolol i nhibited the dispersion response whereas yohimbine did not block the r esponse. Both forskolin and 8-Br-cAMP were effective in dispersing the pigment. Epinephrine was effective in accelerating the aggregation of pigment and this effect was inhibited by yohimbine. These results ind icate that stimulation of beta-adrenoceptors results in an intracellul ar increase in levels of cAMP which then initiates the dispersion of p igment and that alpha-adrenoceptors mediate the aggregation of pigment . These adrenergic mechanisms are similar to those associated with leu cophores in Oryzias. These findings demonstrate that the novel chromat ophores behave physiologically as a type of a leucophore.