Pigment aggregation is triggered by an increase in free calcium ions within fish chromatophores

Abstract 1. 1. When melanophores and erythrophores in primary culture of the platyfish have been treated with A23187 and exposed to a low concentration of Ca 2+ (10 −8 M), pigment granules remained dispersed. 2. 2. Experimental elevation of the cytosolic concentration of Ca 2+ to 10 −4 M caused the aggregation of pigment. 3. 3. When the Quin 2- or Fura 2-loaded melanophores were stimulated by the pigment-aggregating agent, norepinephrine, the fluorescence intensity, as monitored with a fluorimeter, increased. 4. 4. From these observations, it is suggested that the stimulation of α-adrenoceptors by catecholamines is accompanied by an increase in intracellular Ca 2+ level, which, in turn, triggers the aggregation of melanosomes.