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Title: The Chinese soft-shelled turtle, Pelodiscus sinensis, excretes urea mainly through the mouth instead of the kidney
Authors: Ip, Y.K. 
Loong, A.M.
Lee, S.M.L.
Ong, J.L.Y.
Wong, W.P.
Chew, S.F.
Keywords: Ammonia
Buccopharyngeal respiration
Buccopharyngeal villiform processes
Nitrogen metabolism
Urea excretion
Urea transporter
Issue Date: Nov-2012
Citation: Ip, Y.K., Loong, A.M., Lee, S.M.L., Ong, J.L.Y., Wong, W.P., Chew, S.F. (2012-11). The Chinese soft-shelled turtle, Pelodiscus sinensis, excretes urea mainly through the mouth instead of the kidney. Journal of Experimental Biology 215 (21) : 3723-3733. ScholarBank@NUS Repository.
Abstract: The Chinese soft-shelled turtle, Pelodiscus sinensis, is well adapted to aquatic environments, including brackish swamps and marshes. It is ureotelic, and occasionally submerges its head into puddles of water during emersion, presumably for buccopharyngeal respiration. This study was undertaken to test the hypothesis that the buccophyaryngeal cavity constitutes an important excretory route for urea in P. sinensis. Results indicate that a major portion of urea was excreted through the mouth instead of the kidney during immersion. When restrained on land, P. sinensis occasionally submerged their head into water (20-100 min), during which urea excretion and oxygen extraction occurred simultaneously. These results indicate for the first time that buccopharyngeal villiform processes (BVP) and rhythmic pharyngeal movements were involved in urea excretion in P. sinensis. Urea excretion through the mouth was sensitive to phloretin inhibition, indicating the involvement of urea transporters (UTs). In addition, saliva samples collected from the buccopharyngeal surfaces of P. sinensis injected intraperitoneally with saline contained ∼36mmol Nl -1 urea, significantly higher than that (∼2.4mmol Nl -1) in the plasma. After intraperitoneal injection with 20 μmol urea g-1 turtle, the concentration of urea in the saliva collected from the BVP increased to an extraordinarily high level of ∼614 μmol N ml-1, but the urea concentration (∼45 μmol N ml-1) in the plasma was much lower, indicating that the buccopharyngeal epithelium of P. sinensis was capable of active urea transport. Subsequently, we obtained from the buccopharyngeal epithelium of P. sinensis the full cDNA sequence of a putative UT, whose deduced amino acid sequence had ∼70% similarity with human and mouse UT-A2. This UT was not expressed in the kidney, corroborating the proposition that the kidney had only a minor role in urea excretion in P. sinensis. As UT-A2 is known to be a facilitative urea transporter, it is logical to deduce that it was localized in the basolateral membrane of the buccopharyngeal epithelium, and that another type of primary or secondary active urea transporter yet to be identified was present in the apical membrane. The ability to excrete urea through the mouth instead of the kidney might have facilitated the ability of P. sinensis and other soft-shelled turtles to successfully invade the brackish and/or marine environment. © 2012. Published by The Company of Biologists Ltd.
Source Title: Journal of Experimental Biology
ISSN: 00220949
DOI: 10.1242/jeb.068916
Appears in Collections:Staff Publications

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