Using denervated melanophores in isolated scales of the dark chub Zacco temmincki, effects of divalent cations, Ca^<++>, Sr^<++>, Ba^<++>, Mg^<++> and Mn^<++> on responses of the melanophores were investigated.
The Ca^<++> was not required for melanosome aggregation mediated by alpha adrenergic receptors or by melatonin receptors and for melanosome dispersion mediated by beta adrenergic receptors. The Ca^<++> was required for the melanosome-dispersing action of melanophore-stimulating hormone (MSH). Sr^<++>, Ba^<++>, Mg^<++> and Mn^<++> could not replace the Ca^<++>. Mn^<++> reversibly inhibited the action of MSH. These results indicate that the Ca^<++> is the only divalent cation specifically required for MSH action on the melanophores of Z temmincki