title: Can gramicidin ion channel affect the dipole potential of neighboring phospholipid headgroups?
abstract: The cyclic voltammetry behavior of a mercury-supported tethered bilayer lipid membrane (tBLM) incorporating gramicidin A was investigated in aqueous 0.1 M KCl at pH 6.8, 5.4 and 3. The distal leaflet of the lipid bilayer consisted of dioleoylphosphatidylcholine (DOPC), dioleoylphosphatidylserine (DOPS), dioleoylphosphatidic acid or a DOPC/cholesterol mixture. In passing from pH 6.8 to pH 3, the midpoint potential between the negative current peak, due to K(+) inflow into the spacer, and the positive current peak, due to K(+) ejection into the aqueous solution, shifts toward more positive potentials, while the separation between these two peaks decreases. This behavior is interpreted quantitatively on the basis of a model relying on tBLM structural features estimated independently in previous works. The only adjustable parameter is the rate constant for cation translocation across a potential energy barrier located in the hydrocarbon tail region. The behavior is ascribed to a dragging of the lipid headgroups adjacent to the gramicidin channel mouth toward the hydrocarbon tail region, with a resulting decrease in the negative charge of the DOPC phosphate group, or of the DOPS carboxyl group, with decreasing pH.
authors.affiliation: Department of Chemistry "Ugo Schiff", Florence University, Via della Lastruccia 3, Sesto Fiorentino, Firenze, Italy. Electronic address: lucia.becucci@unifi.it.
authors.forename: Lucia
authors.initials: L
authors.lastname: Becucci
authors.affiliation: Department of Chemistry "Ugo Schiff", Florence University, Via della Lastruccia 3, Sesto Fiorentino, Firenze, Italy.
authors.forename: Rolando
authors.initials: R
authors.lastname: Guidelli
mesh_terms: D004563:Electrochemistry / Q000379:methods; D006096:Gramicidin / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008564:Membrane Potentials; D008628:Mercury / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry; D010718:Phosphatidylserines / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D007473:Ion Channels; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D010743:Phospholipids; D014867:Water; D006096:Gramicidin; C042511:1,2-dioleoylphosphatidylserine; C017251:1,2-oleoylphosphatidylcholine; D008628:Mercury
keywords: Cyclic voltammetry; Dioleoylphosphatidylcholine; Dioleoylphosphatidylserine; Surface dipole potential; Tethered bilayer lipid membrane