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This Article Full Text Full Text (PDF) All Versions of this Article: 290/4/F821    most recent 00312.2005v1 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 Tong, Q. Articles by Stockand, J. D. Search for Related Content PubMed PubMed Citation Articles by Tong, Q. Articles by Stockand, J. D.

Functional polymorphisms in the -subunit of the human epithelial Na⁺ channel increase activity

¹Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas; and ²Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati Medical Center, Cincinnati, Ohio

Submitted 2 August 2005 ; accepted in final form 17 October 2005

Activity of the epithelial Na⁺ channel (ENaC) is limiting for Na⁺ reabsorption at the distal nephron. Gain-of-function mutations in ENaC cause Liddle's syndrome: a severe form of inheritable hypertension. Several polymorphisms in -hENaC possibly associated with abnormal Na⁺ handling by the kidney and the salt-sensitive hypertension prevalent in black populations have been reported. The functional effects of -hENaC polymorphisms on channel activity, however, remain controversial and have not been directly tested in a mammalian background. We ask here whether polymorphisms at positions 334, 618, and 663 in -hENaC influence channel activity. Activity of wild-type (A334, C618, A663) and polymorphic ENaC expressed in Chinese hamster ovary cells was assessed with patch-clamp electrophysiology. While the A334T polymorphism had little effect on macroscopic ENaC currents, the C618F and A663T polymorphisms significantly increased ENaC activity >3.3- and 1.6-fold, respectively. Similarly, polymorphic ENaC had greater activity compared with wild-type channels in excised patches with activity of C618F and A663T channels increased 3.8- and 2.6-fold, respectively. Unitary channel conductances and reversal potentials were not different for polymorphic and wild-type ENaC. Increases in activity resulted primarily from increases in the apparent number of active (polymorphic) channels in the plasma membrane. Moreover, addition of a reducing agent to the cytosol significantly increased activity of wild-type ENaC equal to that of C618F polymorphic channels but had no effect on these latter channels. These results are consistent with the C618F and A663T polymorphisms leading to elevated ENaC activity with the possibility that they facilitate altered Na⁺ handling by the kidney.

hypertension; Liddle's syndrome; sequence variations