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Multiple urea transporter proteins in the kidney of holocephalan elephant fish (Callorhinchus milii)

journal contribution
posted on 2023-05-17, 15:50 authored by Kakumura, K, Watanabe, S, Bell, JD, Donald, JA, Toop, T, Kaneko, T, Hyodo, S
Reabsorption of filtered urea by the kidney is essential for retaining high levels of urea in marine cartilaginous fish. Our previous studies on the shark facilitative urea transporter (UT) suggest that additional UT(s) comprising the urea reabsorption system could exist in the cartilaginous fish kidney. Here, we isolated three cDNAs encoding UTs from the kidney of elephant fish, Callorhinchus milii, and termed them efUT-1, efUT-2 and efUT-3. efUT-1 is orthologous to known elasmobranch UTs, while efUT-2 and efUT-3 are novel UTs in cartilaginous fish. Two variants were found for efUT-1 and efUT-2, in which the NH 2-terminal intracellular domain was distinct between the variants. Differences in potential phosphorylation sites were found in the variant-specific NH 2-terminal domains. When expressed in Xenopus oocytes, all five UT transcripts including the efUT-1 and efUT-2 variants induced more than a 10-fold increase in [ 14C] urea uptake. Phloretin inhibited dose-dependently the increase of urea uptake, suggesting that the identified UTs are facilitative UTs. Molecular phylogenetic analysis revealed that efUT-1 and efUT-2 had diverged in the cartilaginous fish lineage, while efUT-3 is distinct from efUT-1 and efUT-2. The present finding of multiple UTs in elephant fish provides a key to understanding the molecular mechanisms of urea reabsorption system in the cartilaginous fish kidney. © 2009 Elsevier Inc. All rights reserved.

History

Publication title

Comparative Biochemistry and Physiology - B Biochemistry and Molecular Biology

Volume

154

Pagination

239-247

ISSN

1096-4959

Department/School

Institute for Marine and Antarctic Studies

Publisher

Pergamon-Elsevier Science Ltd

Place of publication

The Boulevard, Langford Lane, Kidlington, Oxford, England, Ox5 1Gb

Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the biological sciences