Spin-label saturation-recovery EPR at W-band: applications to eye lens lipid membranes

J Magn Reson. 2011 Sep;212(1):86-94. doi: 10.1016/j.jmr.2011.06.014. Epub 2011 Jun 22.

Abstract

Saturation-recovery (SR) EPR at W-band (94 GHz) to obtain profiles of the membrane fluidity and profiles of the oxygen transport parameter is demonstrated for lens lipid membranes using phosphatidylcholine (n-PC), stearic acid (n-SASL), and cholesterol analog (ASL and CSL) spin labels, and compared with results obtained in parallel experiments at X-band (9.4 GHz). Membranes were derived from the total lipids extracted from 2-year-old porcine lens cortex and nucleus. Two findings are especially significant. First, measurements of the spin-lattice relaxation times T1 for n-PCs allowed T1 profiles across the membrane to be obtained. These profiles reflect local membrane properties differently than profiles of the order parameter. Profiles obtained at W-band are, however, shifted to longer T1 values compared to those obtained at X-band. Second, using cholesterol analog spin labels and relaxation agents (hydrophobic oxygen and water-soluble NiEDDA), the cholesterol bilayer domain was discriminated in membranes made from lipids of the lens nucleus. However, membranes made from cortical lipids show a single homogeneous environment. Profiles of the oxygen transport parameter obtained from W-band measurements are practically identical to those obtained from X-band measurements, and are very similar to those obtained earlier at X-band for membranes made of 2-year-old bovine cortical and nuclear lens lipids (M. Raguz, J. Widomska, J. Dillon, E.R. Gaillard, W.K. Subczynski, Biochim. Biophys. Acta 1788 (2009) 2380-2388). Results demonstrate that SR EPR at W-band has the potential to be a powerful tool for studying samples of small volume, ∼30 nL, compared with the sample volume of ∼3 μL at X-band.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Biological Transport, Active
  • Cell Membrane / chemistry
  • Cholesterol
  • Data Interpretation, Statistical
  • Electron Spin Resonance Spectroscopy / methods*
  • Indicators and Reagents
  • Lens, Crystalline / chemistry*
  • Lipid Bilayers / chemistry
  • Membrane Fluidity
  • Membrane Lipids / chemistry*
  • Membranes / chemistry*
  • Oxygen Consumption / physiology
  • Phosphatidylcholines / chemistry
  • Spin Labels
  • Stearic Acids / chemistry
  • Swine

Substances

  • Indicators and Reagents
  • Lipid Bilayers
  • Membrane Lipids
  • Phosphatidylcholines
  • Spin Labels
  • Stearic Acids
  • Cholesterol