Epinephrine-induced changes in the cyclic nucleotide content of fish melanoma cells

Intracellular levels of adenosine 3′,5′-monophosphate (cyclic AMP) and guanosine 3′,5′-monophosphate (cyclic GMP) in melanoma tissues developed in platyfish and swordtail hybrids were determined by radioimmunoassay. The melanoma tissues were composed mostly of pigment cells, many of which responded to epinephrine with pigment aggregation. The aggregated melanosomes redispersed gradually by washing the cells with physiological saline, and rapidly by the perfusion with theophylline. Determination of intracellular levels of cyclic nucleotides revealed that epinephrine produced a small but significant decrease in cyclic AMP level, whereas theophylline elicited a remarkable increase in the intracellular concentration of cyclic AMP. On the other hand, the change in the levels of cyclic GMP was not significant among the tissues subjected to the different experimental conditions. The present results suggest that the centrifugal and centripetal translocations of melanosomes within melanophores are regulated directly by the intracellular concentration of cyclic AMP.