Effect of pressure on the dimyristoylphosphatidylcholine bilayer main transition

Deuterium nuclear magnetic resonance was used to study the effect of pressure on the liquid crystal to gel phase transition in multilamellar vesicles of chain perdeuterated dimyristoylphosphatidylcholine (DMPC-d₅₄). The first spectral moment (M₁), which is proportional to the mean orientational order parameter for the DMPC-d₅₄ acyl chain, was measured as a function of temperature at ambient pressure and at 160 MPa and as a function of pressure at 25 ^∘{}C, 35 ^∘{}C, and 45 ^∘{}C. Application of hydrostatic pressure was found to increase the magnitude of the jump in M₁ at the transition and to reduce the sensitivity of M₁ to temperature just above the transition. These observations suggest that the separation between the observed first-order transition and the critical point for phospholipid bilayers increases with increasing pressure.