Proton currents in K. veneficum differ from all known proton currents in having large inward currents -- a result of the channels opening at membrane potentials about 60 mV more negative than in other species, the researchers found.
"Vertebrate proton channels open to allow acid extrusion, while dinoflagellate proton channels open to allow proton influx into a cell's cytoplasm, making the channel ideally suited to trigger bioluminescence," DeCoursey explained.
When dinoflagellates floating in water are mechanically stimulated by movement, an impulse (action potential) is sent along the membrane of an internal compartment called a vacuole. Clustered along the inside of this membrane are tiny pockets called scintillons, containing a combination of luciferin and luciferase proteins that are able to produce a light flash under the right circumstances. The inside of the vacuole compartment is very acidic and has an abundance of protons.
As the electric impulse travels along the membrane, it causes the voltage-sensitive proton channels to open. Protons then flow from the vacuole into the scintillon, where they react with the luciferase and a flash of light results.
In nonbioluminescent mixotrophic species like K veneficum, proton influx might be involved in prey digestion (e.g., signaling prey capture) or prey capture (e.g., extrusion of stinging trichocysts).
Co-investigator Susan Smith carried out a phylogenetic analysis of
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| Contact: Deb Song deb_song@rush.edu 312-942-0588 Rush University Medical Center Source:Eurekalert |