Alcohol effects on rapid kinetics of water transport through lipid membranes and location of the main barrier

Water permeability of polyunsaturated lipid membranes measured by 17O NMR

Diffusion-controlled water permeation across bilayers of polyunsaturated phospholipids was measured by 17O nuclear magnetic resonance. In 100-nm extruded liposomes containing 50 mM MnCl2, water exchange between internal and external solutions was monitored via changes in the linewidth of the 17O water resonance of external water. Liposome size and shape were characterized by light scattering methods and determination of liposome trapped volume. At 25 degrees C, the following water permeability coefficients were determined: 18:0-18:1n-9 PC, 155 +/- 24 microns/s; 18:0-18:3n-3 PC, 330 +/- 88 microns/s; and 18:0-22:6n-3 PC, 412 +/- 91 microns/s. The addition of 1 M ethanol reduced permeability coefficients to 66 +/- 15 microns/s for 18:0-18:1n-9 PC and to 239 +/- 67 microns/s for 18:0-22:6n-3 PC. Furthermore, the addition of 50 mol% 18:1n-9-18:1n-9 PE reduced the water permeability from 122 +/- 21 microns/s for pure 18:1n-9-18:1n-9 PC to 74 +/- 15 microns/s for the mixture. The significant increase in water permeation for membranes with polyunsaturated hydrocarbon chains correlates with looser packing of polyunsaturated lipids at the lipid-water interface and the suggested deeper penetration of water into these bilayers. Ethanol may block water diffusion pathways by occupying points of water entry into bilayers at the interface. The addition of dioleoylphosphatidylethanolamine increases lipid packing density and, consequently, reduces permeation rates.

The local anesthetic tetracaine destabilizes membrane structure by interaction with polar headgroups of phospholipids

The effect of the local anesthetic tetracaine at less than 10 mM on the water permeability of the phospholipid membrane was examined using liposomes composed of various molar ratios of negatively charged cardiolipin to electrically neutral phosphatidylcholine by monitoring their osmotic shrinkage in hypertonic glucose solution at 30 degrees C. The concentration of tetracaine causing the maximum velocity of shrinkage of liposomes increased with increase in the molar ratio of cardiolipin. Tetracaine increased the zeta-potential of the negatively charged liposomal membrane toward the positive side due to the binding of its cationic form to the negatively charged polar headgroups in the membrane. The maximum velocity of water permeation induced by osmotic shock was observed at essentially the same tetracaine concentration giving a zeta-potential of the liposomal membrane of 0 mV. These concentrations were not affected by change in the sort of acyl-chain of phospholipids in the liposomes when their negative charges were the same. These results suggests that the membrane integrity is governed mainly by the electrical charge of phospholipid polar headgroups when phospholipid bilayers are in the highly fluid state, and that positively charged tetracaine molecules neutralize the negative surface charge, lowering the barrier for water permeation through phospholipid bilayers.

Interaction of surfactants with vesicle membrane of dipalmitoylphosphatidylcholine: fluorescence depolarization study

The effect of surfactants on the "fluidity" of dipalmitoylphosphatidylcholine (DPPC) vesicle membrane was studied by means of the fluorescence depolarization technique with fatty acid fluorescent probes, in which the anthroyloxy group is introduced at different positions along the acyl chain. Three types of surfactants were examined; anionic sodium alkylsulfates, cationic alkyltrimethylammonium chlorides, and non-ionic alkanoyl-N-methylglucamides (MEGA-n). Perturbing effects of the surfactants depended on both the alkyl chain-length and the type of head group. Sodium alkylsulfates with octyl- and decyl-chain and alkyltrimethylammonium chlorides with octyl-, decyl- and dodecyl-chain did not affect the membrane fluidity when incorporated in the membrane, whereas sodium dodecylsulfate and tetradecyltrimethylammonium chloride decreased the membrane fluidity at both gel and liquid crystalline states of the membrane. All the MEGA series surfactants decreased the membrane fluidity, whose perturbing potency was in the order of MEGA-8 less than MEGA-9 approximately equal to MEGA-10. The perturbation at different depths in the membrane by sodium dodecylsulfate and MEGA-9 was also examined. No significant change in the fluidity gradient across the membrane was induced by the addition of these surfactants.

Ethanol and the fluidity of the yeast plasma membrane

Evidence is presented for an exponential increase in yeast plasma membrane fluidity (as measured by passive permeability to acetic acid) with ethanol concentration. The role of adaptation of yeast cells to ethanol can be seen in the existence of a threshold concentration before the onset of an observed fluidizing effect. The physiological state of the yeast cells is also demonstrated to influence the sensitivity of the membrane to fluidization by ethanol. On the basis of these results, the concept that increased fluidity is an adaptive response conferring ethanol tolerance is disputed. An alternative hypothesis, namely that the observed increase in fluidity is the net result of a number of more fundamental changes, is presented to explain the observed effects.

Leakage from egg phosphatidylcholine vesicles induced by Ca2+ and alcohols

The results shown in this paper indicate that the permeability properties of egg yolk phosphatidylcholine sonicated vesicles as detected by the leakage of carboxy fluorescein changes according to the Ca2+ content. Vesicles containing Ca2+ show a higher rate of leakage than those containing Na+ solutions in response to the increase of Ca2+ concentration in the outer solution. The results are interpreted in terms of the rigidity promoted by Ca2+ and are compared to those obtained with long and short chain alcohols.

Stopped-flow rapid kinetics of anesthetic-induced phase transition in phospholipid vesicle membranes: nonlocalized fluctuation

Kinetics of the gel to liquid-crystalline phase transition of dipalmitoylphosphatidylcholine vesicle membrane was studied by the stopped-flow technique with turbidity detection. The observed change in turbidity was well characterized by a single-exponential decay curve with relaxation time in the millisecond range, although the existence of a faster process than the dead-time of the stopped-flow apparatus was inferred from the amplitude analysis. Relaxation times were determined as functions of 1-hexanol concentration and temperature just below phase transition. From the analysis based on the theories of nonequilibrium relaxation, it is concluded that the phase transition induced by 1-hexanol is governed by a nonlocalized fluctuation mechanism. The anesthetic-induced nonequilibrium state is unstable rather than metastable.