STIMULATION OF BIOLUMINESCENCE BY 5-METHOXYLATED INDOLEAMINES IN THE DINOFLAGELLATE, GONYAULAX-POLYEDRA

1. Bioluminescence was measured in cells transferred from a light/dark cycle of 12:12 hr to constant darkness. 2. Gonyaulax responded strongly and specifically to 5-methoxytryptamine and its analogue, N,N-dimethyl-5-methoxytryptamine. The reaction threshold for 5-methoxytryptamine was as low as 2 x 10(-8) M. At 10(-4) M, this indoleamine stimulated bioluminescence by 55-fold. 3. 5-Hydroxylated indoleamines such as serotonin and N-acetyl-serotonin, but also the 5-methoxylated indoleamine, melatonin, and the indole alcohols, 5-hydroxytryptophol and 5-methoxytryptophol were much less effective or without stimulatory potency. 4. The responsiveness of cells to 5-methoxytryptamine differed considerably in various phases of the circadian cycle. The highest degree of stimulation was attained around the middle of subjective night, whereas almost no stimulation was observed during the second part of subjective day.