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This Article Full Text Full Text (PDF) All Versions of this Article: 290/6/F1437    most recent 00449.2005v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Stewart, G. S. Articles by Cooper, G. J. Search for Related Content PubMed PubMed Citation Articles by Stewart, G. S. Articles by Cooper, G. J.

Molecular characterization of the mercurial sensitivity of a frog urea transporter (fUT)

²Department of Biomedical Science, University of Sheffield, Sheffield; and ¹Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom

Submitted 10 November 2005 ; accepted in final form 20 December 2005

The amphibian urea transporter (fUT) shares many properties with the mammalian urea transporters (UT) derived from UT-A and UT-B genes. The transport of urea by fUT is inhibited by the mercurial agent p-chloromercuribenzenesulfonic acid (pCMBS). We found that in oocytes expressing cRNA encoding fUT, a 5-min preincubation in 0.5 mM mercury chloride (HgCl₂) also significantly reduced urea uptake. The transport of urea by fUT was rendered mercury (Hg²⁺) insensitive by mutating either of the residues C185 or H187, both of which lie within the M-I region (close to the hypothetical UT pore). In oocytes expressing a mixture of the C185 and H187 mutants, Hg²⁺ sensitivity was reestablished. The transport of urea by the mouse UTs mUT-A2 and mUT-A3 was not sensitive to Hg²⁺. Introducing cysteine residues analogous to that mutated in fUT into mUT-A2 or mUT-A3 did not induce Hg²⁺ sensitivity. Additionally, introducing the double cysteine, histidine mutations into mUT-A2 or mUT-A3 still did not induce Hg²⁺ sensitivity, indicating that a region outside of the M-I region also contributes to the Hg²⁺-induced block of fUT. Using a series of chimeras formed between UT-A3 and fUT, we found that as well as C185 and H187, residues within the COOH terminal of fUT determine Hg²⁺ sensitivity, and we propose that differences in the folding of this region between fUT and mUT-A2/mUT-A3 allow access of Hg²⁺ to the fUT channel pore.

mercury chloride; Xenopus laevis oocyte