Effect of the structure of cholesterol-based tethered bilayer lipid membranes on ionophore activity.
Tethered bilayer lipid membranes (tBLM) are formed on 1) pure tether lipid triethyleneoxythiol cholesterol (EO(3)C) or on 2) mixed self-assembled monolayers (SAMs) of EO(3)C and 6-mercaptohexanol (6MH). While EO(3)C is required to form a tBLM with high resistivity, 6MH dilutes the cholesterol content in the lower leaflet of the bilayer forming ionic reservoirs required for submembrane hydration. Here we show that these ionic reservoirs are required for ion transport through gramicidin or valinomycin, most likely due to the thermodynamic requirements of ions to be solvated once transported through the membrane. Unexpectedly, electrochemical impedance spectroscopy (EIS) shows an increase of capacitance upon addition of gramicidin, while addition of valinomycin decreases the membrane resistance in the presence of K(+) ions. We hypothesise that this is due to previously reported phase separation of EO(3)C and 6MH on the surface. This results in ionic reservoirs on the nanometre scale, which are not fully accounted for by the equivalent circuits used to describe the system.
Kendall
James K R
JK
School of Physics & Astronomy, University of Leeds, Leeds, LS2 9JT, UK.
Johnson
Benjamin R G
BR
Symonds
Philip H
PH
Imperato
Guiseppi
G
Bushby
Richard J
RJ
Gwyer
James D
JD
van Berkel
Cees
C
Evans
Stephen D
SD
Jeuken
Lars J C
LJ
D002784:Cholesterol / Q000737:chemistry*; D006046:Gold / Q000737:chemistry; D006096:Gramicidin / Q000737:chemistry / Q000494:pharmacology; D017136:Ion Transport; D007476:Ionophores / Q000737:chemistry / Q000494:pharmacology*; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D020349:Surface Plasmon Resonance; D014634:Valinomycin / Q000737:chemistry / Q000494:pharmacology
D007476:Ionophores; D008051:Lipid Bilayers; D006096:Gramicidin; D014634:Valinomycin; D006046:Gold; D002784:Cholesterol; D012964:Sodium; D011188:Potassium