Requirement of Indoleamines and a V-type Proton ATPase for the Expression of the Circadian Glow Rhythm in Gonyaulax polyedra

Abstract

In the dinoflagellate Gonyaulax polyedra, bioluminescence is known to be controlled by proton transfer from an acidic vacuole system to the scintillons. We demonstrate that bafilomycin A 1, a specific blocker of V-type proton ATPases, inhibits at low concentrations (down to 2 × 10 –8 M) bioluminescence and, in particular, the circadian glow maximum. For many hours bafilomycin A 1 does not interfere with the capacity of the bioluminescent system. Therefore, we conclude on the participation of a V-type ATPase in proton accumulation in the acidic vacuoles. Inhibition of tryptophan hydroxylase by p-chlorophenylalanine, p-fluorophenylalanine, or 5-fluorotryptophan also suppresses the circadian glow maximum. After inhibition of the enzyme by p-chlorophenylalanine, the glow peak can be restored, without any additional unspecific effects on bioluminescence, by supplementation with 5-hydroxytryptophan. Therefore, the availability of indoleamines is required for the expression of the glow maximum. Since 5-methoxytryptamine is the only physiologically occurring indoleamine with substantial effects on bioluminescence at low concentrations (below 10 –7 M), and since this substance accumulates in the second half of the night to stimulatory concentrations, this indolic metabolite may represent the physiologically active substance involved in the expression of the glow maximum.