4. Effects of high pressure on cell membranes
Macdonald et al. characterized the membranes of a number of fish
that inhabit a series of water depths using steady-state anisotropy
measurement. Anisotropy of DPH in the brain myelin was distinctly
lower in deep-sea species, indicating a lower order of the membrane
[24]. In liver mitochondria, the ratio of unsaturated fatty acids (UFAs)
to saturated fatty acids showed a significant increase with depth of
capture, implying the acclimation of fish membranes to habitat pressures
by incorporation of unsaturated bonds [8,25].
In our recent study, we analyzed the effect of high pressure on the
membrane properties of enteric bacterium Escherichia coli using
HP-TRFAM [26]. The order parameter S of the TMA-DPH-labeled E. coli
membrane was much higher at a lower temperature (15 °C) than at a
higher temperature (37 °C) (Fig. 3). S linearly increased with increasing
pressure at both temperatures. Correspondingly, the rotational diffusion
coefficient Dw wasmuch higher at 37 °C than at 15 °C, and it linearly decreased
with increasing pressure at both temperatures. The changes in S
and Dw in E. coli cell membrane with increasing pressure is analogous to
those observed in the POPC membrane in the liquid-crystalline phase
(Figs. 2 and 3). Based on the wobbling-in-a-cone model, the angle of
rotational motion of TMA-DPH is assumed to be reduced by 2.7° with a
pressure increase of 50 MPa [26]. This value is comparable to that