Pharmacological investigation of the bioluminescence signaling pathway of the dinoflagellate Lingulodinium polyedrum: evidence for the role of stretch-activated ion channels

Dinoflagellate bioluminescence serves as a whole-cell reporter of mechanical stress, which activates a signaling pathway that appears to involve the opening of voltage-sensitive ion channels and release of calcium from intracellular stores. However, little else is known about the initial signaling events that facilitate the transduction of mechanical stimuli. In the present study using the red tide dinoflagellate Lingulodinium polyedrum (Stein) Dodge, two forms of dinoflagellate bioluminescence, mechanically stimulated and spontaneous flashes, were used as reporter systems to pharmacological treatments that targeted various predicted signaling events at the plasma membrane level of the signaling pathway. Pretreatment with 200 μM Gadolinium III (Gd(3+) ), a nonspecific blocker of stretch-activated and some voltage-gated ion channels, resulted in strong inhibition of both forms of bioluminescence. Pretreatment with 50 μM nifedipine, an inhibitor of L-type voltage-gated Ca(2+) channels that inhibits mechanically stimulated bioluminescence, did not inhibit spontaneous bioluminescence. Treatment with 1 mM benzyl alcohol, a membrane fluidizer, was very effective in stimulating bioluminescence. Benzyl alcohol-stimulated bioluminescence was inhibited by Gd(3+) but not by nifedipine, suggesting that its role is through stretch activation via a change in plasma membrane fluidity. These results are consistent with the presence of stretch-activated and voltage-gated ion channels in the bioluminescence mechanotransduction signaling pathway, with spontaneous flashing associated with a stretch-activated component at the plasma membrane.

Antioxidative protection in a high-melatonin organism: the dinoflagellate Gonyaulax polyedra is rescued from lethal oxidative stress by strongly elevated, but physiologically possible concentrations of melatonin

Lethal oxidative stress was investigated in the dinoflagellate Gonyaulax polyedra by measuring the dying-peak of bioluminescence during circadian phases of low physiological light emission, low bioluminescence capacity, and low sensitivity to stimulatory agents. Measurements were carried out in constant darkness after transfer of cells from light at CT 6 (circadian time, 0600 hr). H2O2 (0.08 mM), when administered 1 hr after transfer of cells, led to a multifold, long-lasting enhancement of light emission, which is typical for lethal cell damage. At the circadian phases of investigation, melatonin did not substantially stimulate bioluminescence up to concentrations of 0.5 mM. At this concentration, addition of melatonin prevented the dying-peak and reduced bioluminescence to almost basal values. The high concentration of melatonin applied is not unphysiological in Gonyaulax, because the indoleamine can increase to levels of several millimolar, e.g., in response to temperature signals. These protective effects of melatonin seem to be caused mainly by the direct action of melatonin as an antioxidant, because the major enzymes of antioxidative protection were not stimulated by melatonin, although some of them responded to H2O2. The activities of neither superoxide dismutase, hemoperoxidase/catalase, glutathione peroxidase, nor haloperoxidase were enhanced under the influence of melatonin; glutathione S-transferase activity increased only slightly.