The action of melatonin on single amphibian pigment cells in tissue culture.

1. Neural crest material from neurula stage Xenopus embryos was tissue cultured as small aggregates of cells or a single cell suspension. Isolated pigment cells differentiated after 2 days in culture. 2. Melatonin (10(-15) to 10(-13) M) induced pigment granule condensation; it was 10,000 times more effective than any other compound tested. 3. Tests with appropriate agents showed the pigment cells to have beta-adrenoceptors and 5-hydroxytryptamine receptors; these sites could be blocked without affecting the response to melatonin. Phentolamine blocked the effect of melatonin. 4. Removal of Na+ or Ca2+ from the bathing medium inhibited melatonin-induced pigment granule condensation; 10 mM K+ induced pigment granule condensation. D600, Mn2+ and La3+, which inhibit Ca2+ entry, blocked the effect of melatonin. 5. Cyclic GMP induced pigment condensation and cyclic AMP pigment dispersion (10(-2) to 10(-4) M). 6. It is suggested that the action of melatonin is accompanied by depolarization and the entry of calcium ions. 7. Pigment cells in tissue culture could provide a useful bioassay method for melatonin.