Changes of intrinsic membrane potentials induced by flip-flop of long-chain fatty acids.
The passive transbilayer movement-flip-flop-was investigated on planar bilayer lipid membranes (BLMs), containing myristic, stearic, or linoleic long-chain fatty acids (FA). In response to a transbilayer pH gradient, a difference in the surface charges between inner and outer leaflets appeared. Because the BLM was formed from FA and neutral lipid, a surface potential difference was originated solely by a concentration difference of the initially equally distributed ionized FA. As revealed by zeta-potential measurements, the corresponding surface potential difference DeltaPhi(s) was at least twice the value expected from a titration of the FA alone. The additional surface charge was attributed to FA flip-flop induced by the transbilayer pH gradient. DeltaPhi(s) was derived from capacitive current measurements carried out with a direct current (dc) bias and was corrected for changes of membrane dipole potential Phi(d). Dual-wavelength ratiometric fluorescence measurements have shown that Phi(d) values of the pure DPhPC bilayers and BLMs containing 40 mol % FA differ by less than 6%. It is concluded that fast FA flip-flop is not restricted to membranes with high curvature. The role of pH gradient as an effective driving force for the regulation of FA uptake is discussed.
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Department of Medical Physics and Biophysics, Martin-Luther-University, 06097 Halle/Saale, Germany. elena.pohl@medizin.uni-halle.de
Peterson
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D002021:Buffers; D005227:Fatty Acids / Q000737:chemistry*; D005230:Fatty Acids, Nonesterified / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes; D008564:Membrane Potentials; D010714:Phosphatidylethanolamines / Q000737:chemistry; D011199:Potentiometry; D011726:Pyridinium Compounds / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013229:Stearic Acids / Q000737:chemistry; D013499:Surface Properties
D002021:Buffers; D005227:Fatty Acids; D005230:Fatty Acids, Nonesterified; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008081:Liposomes; D010714:Phosphatidylethanolamines; D011726:Pyridinium Compounds; D013229:Stearic Acids; C107331:diphytanoylphosphatidylethanolamine; C031183:stearic acid; C050019:1-(3-sulfonatopropyl)-4-(beta)(2-(di-n-butylamino)-6-naphthylvinyl)pyridinium betaine