Gating of amiloride-sensitive Na(+) channels: subunit-subunit interactions and inhibition by the cystic fibrosis transmembrane conductance regulator.
In search of the structural basis for gating of amiloride-sensitive Na(+) channels, kinetic properties of single homo and heterooligomeric ENaCs formed by the subunits with individual truncated cytoplasmic domains were studied in a cell-free planar lipid bilayer reconstitution system. Our results identify the N-terminus of the alpha-subunit as a major determinant of kinetic behavior of both homooligomeric and heterooligomeric ENaCs, although the carboxy-terminal domains of beta- and gamma-ENaC subunits play important role(s) in modulation of the kinetics of heterooligomeric channels. We also found that the cystic fibrosis transmembrane conductance regulator (CFTR) inhibits amiloride-sensitive channels, at least in part, by modulating their gating. Comparison of these data suggests that the modulatory effects of the beta- and gamma-ENaC subunits, and of the CFTR, may involve the same, or closely related, mechanism(s); namely, "locking" the heterooligomeric channels in their closed state. These mechanisms, however, do not completely override the gating mechanism of the alpha-channel.
Berdiev
B K
BK
Department of Physiology and Biophysics and Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama at Birmingham, Birmingham, Alabama 35294-0005, USA.
Shlyonsky
V G
VG
Karlson
K H
KH
Stanton
B A
BA
Ismailov
I I
II
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001483:Base Sequence; D055592:Biophysical Phenomena; D001703:Biophysics; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000494:pharmacology*; D017931:DNA Primers / Q000235:genetics; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D017434:Protein Structure, Tertiary; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015222:Sodium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D017931:DNA Primers; D011994:Recombinant Proteins; D015222:Sodium Channels; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000584:Amiloride