One-celled plankton have long been known to produce blue flashes in the sea at night, but no one has known quite how they do it – until now. The plankton, called dinoflagellates (Karlodinium veneficum), bioluminesce through a mechanism involving voltage-gated proton channels within their membranes, according to a study that showed that chemical or electrical events can open or close these channels. The channels were first proposed back in the 1970s by J. Woodland Hastings of Harvard University in Cambridge, Mass. Now, he and colleagues around the country have confirmed their existence: They have identified dinoflagellate genes similar to those that control voltage-sensitive proton channels to activate important biological mechanisms in humans and in other species. Photographing bioluminescence in single-cell sea creatures is a tricky process, but this cartoon illustrates it fairly well, said Dr. Thomas E. DeCoursey, a researcher at Rush University Medical Center in Chicago. Courtesy of National Science Foundation; produced by NSF artist Zina Deretsky. The bioluminescence mechanism may work this way: As dinoflagellates float, stimulation caused by motion in the surrounding water – such as a crashing wave or the wake from a ship – sends electrical impulses around a compartment within the organism called a vacuole, which holds many protons. These impulses open the proton channels connecting the vacuole to tiny pockets called scintillons on the vacuole’s membrane. Once the channels are open, they may funnel protons from the vacuole into the scintillons, activating the protein luciferase stored there and causing flashes of light. The flashes are most visible during dinoflagellate blooms. The researchers mined the gene sequence library of the K. veneficum dinoflagellate and found one gene, called kHv1, that is similar to those already known to code for proton channels in other species. Electrophysiological tests confirmed that the genetically coded protein is indeed a proton channel, but with a significant difference: Proton channels in K. veneficum have large inward currents. The gene that causes the dinoflagellates’ dazzling blue spectacle also is found in the tiny creatures that cause red tides, which are sometimes harmful to the environment. Future investigation into these proton channels might lead to better control of the types of dinoflagellate blooms that pose a threat to the ocean. The findings were reported in the Nov. 1, 2011, issue of Proceedings of the National Academy of Sciences.