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

Wideline deuterium nuclear magnetic resonance was used to investigate the p hase behaviour of bilayer dispersions of chain-perdeuterated dipalmitoylpho sphatidylcholine (DPPC-d(62)) and DPPC-d(62) containing 28.5 mol% cholester ol 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 a mbient 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 isot hermal scans produced observations that suggest two possible refinements to previously reported DPPC-d(62) pressure-temperature phase diagrams. In con trast to DPPC-d(62), which displays at least three transitions as temperatu re is lowered from 90 degrees C to 0 degrees C at a fixed pressure of 210 M Pa, the sample containing 28.5 mol% cholesterol displayed a continuous chan ge from fluid to ordered over a wide temperature range for 210 MPa and belo w. These observations suggest that pressure does not induce any substantial repositioning of cholesterol in the bilayer over the range of conditions s tudied and that cholesterol reduces the sensitivity of bilayer properties t o pressure.