Functional reconstitution of a chloride channel protein from bovine trachea.

Academic Article

Abstract

  • We characterized the electrophysiological properties of a chloride channel protein isolated from bovine trachea after incorporation into planar lipid bilayers, and studied the effects of thiol-modulating agents on channel regulation both in bilayers and vesicular iodide uptake studies. Our experiments showed that this protein formed perfectly anion-selective channels in the bilayer, with an anion permeability sequence of I- (2.1) > NO3- (1.7) > Br- (1.2) > Cl- (1.0). The conductance of this channel was 25-30 picosiemens in 150 mM Cl-, and saturated with increasing chloride concentration. This channel could be completely inhibited by 4,4'-bis(isothiocyano)-2,2'-stilbenedisulfonate. Immunoblot analysis, using polyclonal antibodies (anti-p38), revealed one major band at 140 kDa. Upon reduction with dithiothreitol, 64- and 38-kDa polypeptides were observed. Functional experiments showed that reduction was accompanied by loss of 125I- uptake and single-channel activity. In the presence of dithiothreitol, only the low molecular mass protein forms (64 and 38 kDa) were detected by anti-p38 antibodies on Western blots. Cross-linking of S-S bonds with Cu(2+)-o-phenanthroline led to activation of chloride channels in vesicles and bilayers. Over-aggregation of chloride channels by this S-S cross-linking reagent caused inhibition of 125I- uptake by 80-100% and the abolishment of single-channel activity. We propose that the native chloride channel from bovine trachea can exist in vivo in different structural and functional forms depending upon its thiol-disulfide oxidation reduction status. The oxidized form has a molecular mass of 140 kDa and represents a fully active chloride channel. Inactivation of this channel might occur by over-aggregation of protein subunits, or by dissociation of the 140-kDa subunit by disulfide bond reduction.
  • Published In

    Keywords

  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid, 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid, Animals, Blotting, Western, Cattle, Chloride Channels, Dithiothreitol, Electric Conductivity, Electrophoresis, Polyacrylamide Gel, Ion Channels, Kinetics, Lipid Bilayers, Macromolecular Substances, Membrane Potentials, Membrane Proteins, Muscle, Smooth, Proteolipids, Time Factors, Trachea
  • Author List

  • Ran S; Fuller CM; Arrate MP; Latorre R; Benos DJ
  • Start Page

  • 20630
  • End Page

  • 20637
  • Volume

  • 267
  • Issue

  • 29