Figure 17.
Proton channels trigger a light flash in bioluminescent dinoflagellates in response to mechanical stimulation. An action potential travels along the tonoplast, the membrane surrounding the large central flotation vacuole, and invades the scintillon, a small organelle that contains high concentrations of luciferin, luciferase, and luciferin binding protein. The depolarization opens voltage-gated proton channels in the scintillon membrane. The resulting proton influx from the vacuole (at pH 3.5–4.5; Refs. 374, 380) directly triggers the flash both by activating luciferase and by causing LBP to release luciferin, the substrate for luciferase. A proton channel with properties like those in kHV1 (FIGURES 18 AND 19) could also mediate the action potential. [From Hastings (202).]