Nitric oxide decreases ammonium release in tadpoles of the clawed frog, <Emphasis Type="Italic">Xenopus laevis</Emphasis>, Daudin |
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Authors: | Stefan Wildling Hubert H Kerschbaum |
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Institution: | (1) Division of Animal Physiology, Department of Cellular Biology, University of Salzburg, 5020 Salzburg, Austria |
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Abstract: | In the present study, we quantified the physiological consequences of nitric oxide (NO) on ammonium release in tadpoles of
Xenopus laevis. Tadpoles exposed to S-nitro-N-acetylpenicillamine (SNAP), an NO-donor, or l-arginine, the substrate of NO synthase (NOS), showed a reversible decrease, whereas animals exposed to the NOS inhibitor Nω-methyl-l-arginine (l-NMMA) exhibited an increase in ammonium release. Release of ammonium may be of physiological relevance during stress response
of the animal. Handling of tadpoles as well as exposure to hyposmotic environments increased ammonium release. To localize
NO synthesizing cells, we used diaminofluorescein-diacetate (DAF-2DA), an NO-sensitive fluorescent dye, and NADPH-diaphorase
histochemistry, an indicator for NOS activity. We observed a fluorescence signal as well as NADPH-diaphorase activity in small,
solitary cells in the epidermis. Similarly to NADPH-diaphorase histochemistry, silver nitrate staining and rhodamine labelling,
markers for mitochondria-rich cells, showed a strong reaction in these cells. These observations indicate that NO (1) inhibits
ammonium release, and (2) is endogenously synthesized in mitochondria-rich cells in Xenopus tadpoles. Based on our histochemical results, we speculate that gill epithelium and epidermis work in parallel to release
ammonium as epidermal tissue contains mitochondria-rich and NADPH-diaphorase positive cells. |
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Keywords: | Ammonium Nitric oxide NADPH-diaphorase Epidermis Tadpoles Xenopus laevis |
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