pH alterations "reset" Ca2+ sensitivity of brain Na+ channel 2, a degenerin/epithelial Na+ ion channel, in planar lipid bilayers.

Academic Article

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+).
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    Keywords

  • Acid Sensing Ion Channels, Animals, Brain, Calcium, Chelating Agents, Cloning, Molecular, Degenerin Sodium Channels, Egtazic Acid, Epithelial Sodium Channels, Hydrogen-Ion Concentration, Ion Channels, Kinetics, Lipid Bilayers, Membrane Proteins, Nerve Tissue Proteins, Oocytes, Point Mutation, Protein Binding, Sodium Channels, Xenopus
  • Digital Object Identifier (doi)

    Author List

  • Berdiev BK; Mapstone TB; Markert JM; Gillespie GY; Lockhart J; Fuller CM; Benos DJ
  • Start Page

  • 38755
  • End Page

  • 38761
  • Volume

  • 276
  • Issue

  • 42