THE ACTION OF MELATONIN ON SINGLE AMPHIBIAN PIGMENT CELLS IN TISSUE CULTURE

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Abstract
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 β-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.

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