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 chromatophores are leucophores with granular pigment organelles [13]. In the present experiments, adrenergic mechanisms controlling the migration of pigment associated with these chromatophores were investigated. K+ ions induced dispersion of the pigment. The dispersion was prevented by propranolol, an adrenergic blocker, and was absent from denervated preparations, suggesting that the chromatophores are innervated by adrenergic nerves. Adrenergic agonists, namely, isoproterenol and norepinephrine but not epinephrine, induced the dispersion of pigment. Propranolol inhibited the dispersion response whereas yohimbine did not block the response. 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 indicate that stimulation of beta-adrenoceptors results in an intracellular increase in levels of cAMP which then initiates the dispersion of pigment and that alpha-adrenoceptors mediate the aggregation of pigment. These adrenergic mechanisms are similar to those associated with leucophores in Oryzias. These findings demonstrate that the novel chromatophores behave physiologically as a type of a leucophore.