Nematocysts (also known as cnidocysts) of jellyfish and other cnidarians are giant exocytotic organelles of the stinging cells used for prey capture and defense. These miniature cellular weapons contain a cocktail of hemolytic and neurotoxic poisons, making some cnidarians the most venomous animals known. Injection of the toxins requires an effective release mechanism that breaks the physical barrier of the prey's outer-surface tissue. It was known already that a high pressure (15 MPa) drives nematocyst discharge, and that stylets can penetrate even thick crustacean shells. However, neither the kinetics nor the forces involved were known, simply because discharge is so fast that it had not been previously resolved by conventional high-speed imaging.
To clarify these issues, the researchers studied nematocyst discharge with an electronic framing-streak camera at a framing rate of 1,430,000 frames per second. They show discharge kinetics of nematocysts in Hydra to be as short as 700 nanoseconds, creating an acceleration of up to 5,410,000 g. The researchers calculate that although the accelerated mass is very small (~1 nanogram), a pressure generated at the site of impact is more than 7 GPa, which is in the range of that generated by some bullets, and sufficient to penetrate the cuticle of crustacean prey. The researchers propose that the high speed of discharge is caused by the release of energy stored in the stretched configuration of the collagen-polymer of the nematocyst capsule wall. This ingenious solution allows the cellular process of vesicle exocytosis to release kinetic energy in the nanosecond range by a powerful molecular spring mechanism.
Timm Nüchter of University of Frankfurt in Frankfurt am Main, Germany; Martin Benoit of LM University Munich in München, Germany; Ulrike Engel of Darmstadt University of Technology in Darmstadt, Germany and University of Heidelberg in Heidelberg, Germany; Suat Özbek of University of Heidelberg in Heidelberg, Germany; Thomas W. Holstein of University of Frankfurt in Frankfurt am Main, Germany, Darmstadt University of Technology in Darmstadt, Germany, and University of Heidelberg in Heidelberg, Germany.
This work was supported by the DFG and Hamamatsu Photonics Germany.
Nüchter et al.: "Nanosecond- scale kinetics of nematocyst discharge." Publishing in Current Biology 16, R316-R318, May 9, 2006. DOI 101016/j.cub.2006.03.089 www.current-biology.com