Alpha(1)- and alpha(2)-adrenoceptor mediation in melanosome aggregation in cryptic patterning of Pleuronectes americanus

The dark upper (ocular) surface of winter flounder (Pleuronectes americanus) possesses a chromatophore pattern, with cryptic dark bands and white spots, and a general background component, with melanophores under adrenergic neural control. In vitro responsiveness to the alpha-adrenoceptor agonists phenylephrine and clonidine and to the antagonists yohimbine and prazosin demonstrates that melanosome aggregation in this species is mediated through both alpha(1)- and alpha(2)-adrenoceptors, the alpha(2)-subtype being predominant in each pattern component. However, differences in the potency of agonists and antagonists indicate variability in the balance between the two receptors between pattern components. This paper demonstrates that it cannot be generalized that teleost melanophore alpha-adrenoceptors are universally of one subtype, and also that there is intraspecific variation in subtypes of these receptors associated with the flatfish cryptic patterning mechanism.