The events which trigger the activation of nematocytes are still poorly understood, and no evidence has been presented so far on either the nature of the activatory signal for the nematocyte or the transduction mechanism. In this paper, we present evidence for a role of NO in the discharge of acontial nematocytes. A citrulline-forming enzymatic activity, significantly decreased by the NO synthase inhibitor Nomega-nitro-l-arginine (l-NNA) and by the Ca2+-chelating agent EGTA, was found in the acontial tissue of Aiptasia diaphana. Staining for NADPH diaphorase suggested that NO synthase is localized in supporting cells surrounding the nematocytes. The ability of K+ to induce the discharge of nematocytes in situ could be abolished by preincubation of acontia with l-NNA and restored by addition of excess l-arginine. Direct measurements on K+-induced discharging nematocytes in situ confirmed that NO was released by stimulated acontia. Both in situ and isolated acontial nematocytes promptly discharged when perfused with an aqueous solution of NO. The responsiveness to NO of isolated nematocytes was not abolished in Ca2+-free medium or by treatment with La3+, a well-known Ca2+ channel inhibitor. Since the discharge of in situ nematocytes is known to be Ca2+-dependent, it is proposed that activation of in situ acontial nematocytes is triggered by a Ca2+-dependent release of NO from supporting and/or sensory cells.
In the field: an interview with Sönke Johnsen
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Sönke Johnsen is a Professor at Duke University, USA, investigating visual ecology and he talks about his experiences of collecting transparent animals while blue water diving and in a submersible, as well as outrunning Hurricane Katrina.
Call for new preLighters
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preLights is the preprint highlighting community supported by The Company of Biologists. At the heart of preLights are our preLighters: early-career researchers who select and write about interesting new preprints for the research community. We are currently looking for new preLighters to join our team. Find out more and apply here.
Graham Scott in conversation with Big Biology
Graham Scott talks to Big Biology about the oxygen cascade in mice living on mountaintops, extreme environments for such small organisms. In this JEB-sponsored episode, they discuss the concept of symmorphosis and the evolution of the oxygen cascade.
Cleaner fish are potential super-spreaders
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Bluestreak cleaner wrasse spend their days pecking parasites off the skins of other fish, but now Pauline Narvaez & co have found that they may also be inadvertent super-spreaders. Parasitic flatworms can hitch a ride on the cleaners to reach their next host.
Hearing without a tympanic ear
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In their Review, Grace Capshaw, Jakob Christensen-Dalsgaard and Catherine Carr explore the mechanisms of hearing in extant atympanate vertebrates and the implications for the early evolution of tympanate hearing.
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