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Am J Physiol Cell Physiol 281: C64-C74, 2001;
0363-6143/01 $5.00
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Vol. 281, Issue 1, C64-C74, July 2001

Point mutations in the post-M2 region of human alpha -ENaC regulate cation selectivity

Hong-Long Ji, Suzanne Parker, Anne Lynn B. Langloh, Catherine M. Fuller, and Dale J. Benos

Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35294-0005

We tested the hypothesis that an arginine-rich region immediately following the second transmembrane domain may constitute part of the inner mouth of the epithelial Na+ channel (ENaC) pore and, hence, influence conduction and/or selectivity properties of the channel by expressing double point mutants in Xenopus oocytes. Double point mutations of arginines in this post-M2 region of the human alpha -ENaC (alpha -hENaC) led to a decrease and increase in the macroscopic conductance of alpha R586E,R587Ebeta gamma - and alpha R589E,R591Ebeta gamma -hENaC, respectively, but had no effect on the single-channel conductance of either double point mutant. However, the apparent equilibrium dissociation constant for Na+ was decreased for both alpha R586E,R587Ebeta gamma - and alpha R589E,R591Ebeta gamma -hENaC, and the maximum amiloride-sensitive Na+ current was decreased for alpha R586E,R587Ebeta gamma -hENaC and increased for alpha R589E,R591Ebeta gamma -hENaC. The relative permeabilities of Li+ and K+ vs. Na+ were increased 11.25- to 27.57-fold for alpha R586E,R587Ebeta gamma -hENaC compared with wild type. The relative ion permeability of these double mutants and wild-type ENaC was inversely related to the crystal diameter of the permeant ions. Thus the region of positive charge is important for the ion permeation properties of the channel and may form part of the pore itself.

ion permeability; oocyte; voltage clamp; site-directed mutagenesis; patch clamp; sodium channels; amiloride


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