The Roles of Ca2+ and cAMP in the Nematocyst Discharge of the Sea Anemone Tentacle

The phylum Cnidarians are aquatic animals, including jellyfish, hydra, sea anemones, and corals. They are the simplest metazoans having a nervous system and are diploblastic. Cnidarians are obligate predators that capture prey using specialized stinging cells called cnidocytes. The cnidocyte contains a nematocyst, which is a capsule containing an inverted, hollow tubule. Prey contacting the tentacle triggers the nematocyst tubule to rapidly evert; a process called discharge. The everting tubule penetrates and envenomates the prey, which is carried to the mouth by tentacle movements. Generally both chemical and mechanical stimuli are needed to trigger discharge. The cnidocytes, in sea anemones, are surrounded by two or more supporting cells that have chemoreceptors and possibly contact-sensitive mechanoreceptors (CSMs). Therefore, the cnidocyte/supporting cell complex (CSCC) controls nematocyst discharge. This project explores the chemoreceptor signaling pathway controlling nematocyst discharge from tentacles of the sea anemone, Aiptasia pallida. Chemoreceptors respond to N-acetylated sugars, such as N-acetylneuraminic acid (NANA), which occur on prey surfaces. When stimulated, this chemosensory pathway sensitizes CSMs to trigger nematocyst discharge in response to physical contact. Indirect evidence suggested that the NANA chemosensory pathway acts through the intracellular second-messenger, cyclic-AMP (cAMP). We now show that NANA dose-dependently increases in situ cAMP levels in the ectodermal layer of tentacles from A. pallida, but has no effect on the endodermal cAMP content. In addition, NANA activates cAMP-dependent protein kinase (PKA) in whole tentacle homogenates. High levels of extracellular Mg2+ are commonly used to anesthetize excised tentacles and to block discharge. We find that high levels of Mg2+ block the NANAstimulated cAMP increase. This supports the fact that high Mg2+ levels inhibit nematocyst discharge, but calls into question published findings in which NANAinduced changes in stereociliary bundle length of excised, Mg2+ -anesthetized tentacles are attributed to cAMP. We also find that NANA stimulates calcium influx into isolated tentacle ectodermal cells and that the influx is sensitive to various L-type calcium channel blockers, including dihydropyridines. The coincidence of the desensitization region of the nematocyst discharge curve with those NANA concentrations that most stimulate calcium influx, suggests a role of NANA-stimulated calcium influx in desensitization

Pretreatment with remifentanil protects against the reduced-intestinal contractility related to the ischemia and reperfusion injury in rat

BACKGROUND AND OBJECTIVES: Serious functional and structural alterations of gastrointestinal tract are observed in failure of blood supply, leading to gastrointestinal dismotility. Activation of opioid receptors provides cardioprotective effect against ischemia-reperfusion (I/R) injury. The aim of the present study was to determine whether or not remifentanil could reduce I/R injury of small intestine. METHODS: Male Wistar Albino rats were subjected to mesenteric ischemia (30 min) followed by reperfusion (3 h). Four groups were designed: sham control; remifentanil alone; I/R control; and remifentanil + I/R. Animals in remifentanil + I/R group were subjected to infusion of remifentanil (2 ug kg-1 min-1) for 60 min, half of which started before inducing ischemia. Collecting the ileum tissues, evaluation of damage was based on contractile responses to carbachol, levels of lipid peroxidation and neutrophil infiltration, and observation of histopathological features in intestinal tissue. RESULTS: Following reperfusion, a significant decrease in carbachol-induced contractile response, a remarkable increase in both lipid peroxidation and neutrophil infiltration, and a significant injury in mucosa were observed. An average contractile response of remifentanil + I/R group was significantly different from that of the I/R group. Lipid peroxidation and neutrophil infiltration were also significantly suppressed by the treatment. The tissue samples of the I/R group were grade 4 in histopathological evaluation. In remifentanil + I/R group, on the other hand, the mucosal damage was moderate, staging as grade 1. CONCLUSIONS: The pretreatment with remifentanil can attenuate the intestinal I/R injury at a remarkable degree possibly by lowering lipid peroxidation and leukocyte infiltration

Pretreatment with mineralocorticoid receptor blocker reduces intestinal injury induced by ischemia and reperfusion: involvement of inhibition of inflammatory response, oxidative stress, nuclear factor kappa B, and inducible nitric oxide synthase

WOS: 000341358100016PubMed: 24862878Background: Spironolactone (Sp), a mineralocorticoid receptor antagonist, protects against the ischemia reperfusion (IR) injury of retina, kidney, heart, and brain. We aimed to investigate the effects of Sp on intestinal IR injury. Methods: Male Wistar rats were randomly divided into: (1) a sham control group; (2) an IR control group, subjected to 30 min ischemia and 3 h reperfusion; (3) a group treated with Sp (20 mg/kg) for 3 d before the IR; and (4) a sham-operated control group treated with Sp (20 mg/kg). After the reperfusion, blood and intestinal tissue samples were collected to evaluate histopathologic state, neutrophil infiltration (by measuring myeloperoxidase activity), levels of the cytokines (tumor necrosis factor alpha, interleukin 1 alpha [IL-1 alpha], interferon gamma, monocyte chemotactic protein-1, granulocyte macrophage-colony stimulating factor, and IL-4), malondialdehyde (MDA) and reduced glutathione contents, and immunohistochemical expressions of nuclear factor kappa B, inducible nitric oxide synthase (iNOS), and caspase-3. Results: MDA content, myeloperoxidase activity, and plasma levels of tumor necrosis factor alpha, IL-1 alpha, and monocyte chemotactic protein-1 were all elevated in IR, indicating the oxidative stress and local and systemic inflammatory response. Sp administration markedly reduced the MDA content and the cytokine levels. The pretreatment alleviated intestinal injury, neutrophil infiltration, and the expressions of caspase-3, iNOS, and NF kappa B. Conclusions: The results implicate that Sp may have a strong protective effect against the intestinal IR injury. The effect can be mediated via suppression of both systemic inflammatory response and apoptosis through amelioration of oxidative stress and generation of proinflammatory cytokines, iNOS, caspase-3, and nuclear factor kappa B. Therefore, mineralocorticoid receptor antagonism might be of potential therapeutic benefit in cases of intestinal IR damage. (C) 2014 Elsevier Inc. All rights reserved