Comparative studies of extra-renal organs in cephalopods:ammonia excretion in gills
| Autor: | Po-Hsuan Sung, 宋帛軒 |
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| Rok vydání: | 2016 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 104 Regulation of ammonia homeostasis is essential for cephalopods since protein is the major constituent of their diet and large amounts of ammonia will be produced by extensive amino acid catabolism. Cephalopods have successfully evolved different lifestyles to accommodate their own specific ecological niches in benthic and pelagic habitats. The cephalopod gill has been suggested to represent the major excretory organ thus we hypothesize that cephalopods evolved diverse mechanisms for ammonia regulation depending on their different lifestyles. We developed an in vitro system to study branchial NH4+ transport by using perfusion technic in isolated gills of octopus (Octopus vulgaris), cuttlefish (Sepia pharanois) and squid (Sepioteuthis lessoniana). The gills in all three species possess a bi-phasic NH4+ regulation. In octopus and cuttlefish gills, NH4+ is excreted at blood NH4+ levels higher than 300 μM and increased via ammoniagenesis at NH4+ levels lower than 300 μM. In contrast, squid gills excreted NH4+ at blood NH4+ level higher than 100 μM and accumulated NH4+ at blood NH4+ levels loer than 100 μM. Further experiments simulating extracellular acidosis (pH 7.2) demonstrated that the machinery of H+ secretion coupled with NH4+ excretion can be only observed in octopus gills. Moreover, the rates of NH4+ excretion were higher in squid gills compared to the other two species. The in vivo NH4+ levels were higher (~ 300 μM) in octopus and cuttlefish blood compared to those of squid (~ 25 μM). These observations inferred that the variations in ammonia homeostasis in these three octopus species are probably linked to their respective locomotory capacities. Moreover, pharmacological studies were also used to investigate the ammonia excretion mechanisms and the NH4+ regulation involved in cAMP-dependent pathways were also found in octopus and cuttlefish gills. The present study applied a new method to better understand the mechanisms of ammonia regulation in highly ammonotelic species. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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