2H NMR studies of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylcholine-cholesterol bilayers at high pressure

Wideline deuterium nuclear magnetic resonance was used to investigate the phase behaviour of bilayer dispersions of chain-perdeuterated dipalmitoylphosphatidylcholine (DPPC-d(62)) and DPPC-d(62) containing 28.5 mol% cholesterol for temperatures between 0 degrees C and 90 degrees C and pressures from ambient to 270 MPa. Spectra were obtained over a range of temperature at ambient pressure, 100 MPa, and 210 MPa and over a range of pressure at fixed temperatures of 0 degrees C and 45 degrees C (40 degrees C for the sample containing cholesterol). The combination of complementary isobaric and isothermal scans produced observations that suggest two possible refinements to previously reported DPPC-d(62) pressure-temperature phase diagrams. In contrast to DPPC-d(62), which displays at least three transitions as temperature is lowered from 90 degrees C to 0 degrees C at a fixed pressure of 210 MPa, the sample containing 28.5 mol% cholesterol displayed a continuous change from fluid to ordered over a wide temperature range for 210 MPa and below. These observations suggest that pressure does not induce any substantial repositioning of cholesterol in the bilayer over the range of conditions studied and that cholesterol reduces the sensitivity of bilayer properties to pressure.