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Watch that stinger, if you can...

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One of the fastest biological processes known to man — that of the jellyfish sting — now has been captured on camera. Thomas W. Holstein and his colleagues at the University of Heidelberg in Germany recently recorded the phenomenon.

Organisms in the phylum Cnidaria have nematocysts, or stingers, that contain a mixture of hemolytic and neurotoxic poisons. The toxins can be discharged with a pressure of about 15 MPa, enough to penetrate even the thick outer shells of a crustacean and to cause a great deal of pain.

The tentacles of a polyp Hydra contain hundreds of painful stinging nematocysts. Researchers studying the sting process found that the nematocystscan accelerate millions of times faster than gravity and that they generate 7 GPa of pressure upon impact, roughly equivalent to that produced by some bullets. All of this occurs in 700 ns.

The researchers studied the cnidarian Hydra oligactis and H. vulgaris, whose tentacles have hundreds of nematocysts each. They cultured the tentacles at a temperature of 18 ±1 °C and placed them on a slide attached to two gold or aluminum electrodes spaced 1 cm apart. The electrodes produced an electronic pulse of 0.4 kV/m, 50 to 100 μs long. This pulse, for the experiment, triggered the nematocyst discharge.

A schematic of a nematocyst shows the steps involved when a jellyfish stings its prey (A). Nematocytes comprise a cyst (pink) that contains a minicollagen wall, a tubule and a hatchlike opening from which stylets (black) eject, piercing the prey (A, left). A two-photon micrograph (A, right) shows microtubules anchoring the capsule (tubulin antibody, green; DAPI-stained nucleus, red). A high-speed camera in framing mode captured sequential images at 1.43 million fps; arrows indicate progress of discharge (B). The same camera in streak mode shows, at 3-μs resolution, the ejection of the stylets (arrow), followed by wall contraction (red circle), a short arrest phase (red arrowhead) and tubule eversion (C). Micrograph on left shows slit position (red brackets) during discharge. Courtesy of Cell Press.

They used a Hamamatsu framing/streak camera, which can capture up to 1.43 million frames per second, and a cooled Hamamatsu CCD camera. The instruments produced reliable information on the kinetics and forces involved in the stinging process.

The investigators found that the tip of the nematocyst travels about 13 μm in roughly 700 ns, yielding an average velocity between 9.3 and 18.6 m/s, a final velocity of approximately 18.5 to 37.1 m/s, and a kinetic energy of approximately 0.17 to 0.7 μJ.

Via a photocathode, the camera used to capture jellyfish stings converted photons into electrons that were accelerated by the electrodes, deflected by either the streak or the framing deflection plates, amplified thousands of times by a multichannel plate, and moved to a phosphor screen and converted into an optical image. Courtesy of Cell Press.

The acceleration is more than 5 million times greater than gravity, and the researchers believe that it is produced by vesicle exocytosis, which releases stored energy from the contraction of the minicollagen polymer nematocyst walls. The tip has a mass of about 1 ng and an accelerating force of between 13.2 and 53.1 μN. It can reach its target with a pressure at the penetration site roughly equivalent to that produced by some bullets, or more than 7 GPa.

The results, published in the May 9 issue of Current Biology, also show that this process seems to slow as the level of calcium ions present in the culturing medium drops.

Jul 2006

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