title: pH alterations "reset" Ca2+ sensitivity of brain Na+ channel 2, a degenerin/epithelial Na+ ion channel, in planar lipid bilayers.
abstract: Members of the degenerin/epithelial Na(+) channel superfamily of ion channels subserve many functions, ranging from whole body sodium handling to mechanoelectrical transduction. We studied brain Na(+) channel 2 (BNaC-2) in planar lipid bilayers to examine its single channel properties and regulation by Ca(2+). Upon incorporation of vesicles made from membranes of oocytes expressing either wild-type (WT) BNaC-2 or BNaC-2 with a gain-of-function (GF) point mutation (G433F), functional channels with different properties were obtained. WT BNaC-2 resided in a closed state with short openings, whereas GF BNaC-2 was constitutively activated; a decrease in the pH in the trans compartment of the bilayer activated WT BNaC-2 and decreased its permeability for Na(+) over K(+). Moreover, these maneuvers made the WT channel more resistant to amiloride. In contrast, GF BNaC-2 did not respond to a decrease in pH, and its amiloride sensitivity and selectivity for Na(+) over K(+) were unaffected by this pH change. Buffering the bathing solutions with EGTA to reduce the free [Ca(2+)] to <10 nm increased WT single channel open probability 10-fold, but not that of GF BNaC-2. Ca(2+) blocked both WT and GF BNaC-2 in a dose- and voltage-dependent fashion; single channel conductances were unchanged. A drop in pH reduced the ability of Ca(2+) to inhibit these channels. These results show that BNaC-2 is an amiloride-sensitive sodium channel and suggest that pH activation of these channels could be, in part, a consequence of H(+) "interference" with channel regulation by Ca(2+).
authors.affiliation: Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35294-0005, USA.
authors.forename: B K
authors.initials: BK
authors.lastname: Berdiev
authors.forename: T B
authors.initials: TB
authors.lastname: Mapstone
authors.forename: J M
authors.initials: JM
authors.lastname: Markert
authors.forename: G Y
authors.initials: GY
authors.lastname: Gillespie
authors.forename: J
authors.initials: J
authors.lastname: Lockhart
authors.forename: C M
authors.initials: CM
authors.lastname: Fuller
authors.forename: D J
authors.initials: DJ
authors.lastname: Benos
mesh_terms: D062565:Acid Sensing Ion Channels; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D003001:Cloning, Molecular; D062626:Degenerin Sodium Channels; D004533:Egtazic Acid / Q000494:pharmacology; D053503:Epithelial Sodium Channels; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000737:chemistry*; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism*; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D017354:Point Mutation; D011485:Protein Binding; D015222:Sodium Channels / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D014981:Xenopus
chemical_list: C568267:ASIC1 protein, mouse; D062565:Acid Sensing Ion Channels; D002614:Chelating Agents; D062626:Degenerin Sodium Channels; D053503:Epithelial Sodium Channels; D007473:Ion Channels; D008051:Lipid Bilayers; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D015222:Sodium Channels; D004533:Egtazic Acid; D002118:Calcium