Cell membranes and multilamellar vesicles: Influence of pH on solvent induced damage

Abstract

Pigment leakage from sheep and horse erythrocytes and from red beet tissue induced by non-polar solvents was determined as a function of pH. The results were compared to disruption of multilamellar vesicles (MLV) composed of phospholipids with equimolar cholesterol under identical conditions of solvent exposure and pH. Solvent access to cholesterol was used to measure vesicle disruption. MLV were made from 1,2-dioleoyl phosphatidylethanolamine, sphingomyelin (SP) and various phosphatidylcholines to simulate the major lipid components of membranes. Pigment leakage from erythrocytes caused by petroleum hydrocarbon (b.p. 60-80 degrees C) was maximal at pH 2-4 and at pH 10, but minimal at pH 6.8; alcohols caused less pigment leakage than petroleum hydrocarbon. Beta-cyanin leakage from beet tissue induced by petroleum hydrocarbon was maximal at pH 2, with very little leakage at pH 4, 6.6 and pH 10. Alcohols caused minimal damage to beet tissue above pH 2. Cholesterol removal by petroleum hydrocarbon from MLV of mixed lipid composition was maximal at pH 2-4, reduced at pH 6.8 and minimal at pH 10. Lipid mixtures in which fatty acyl side chains of one phospholipid were of a different length than the other lost more sterol than mixtures in which the acyl side chains were of identical chain length. MLV with more than 25% SP lost more sterol than those with less or no SP. Results show that in mixtures of phospholipids, SP exposes the hydrocarbon phase of a bilayer to solvent extraction, a property that was also observed in native membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Macrophages use a bet-hedging strategy for antimicrobial activity in phagolysosomal acidification

“…Acidification is achieved by pumping protons into the vacuole, and achieving lower pHs against an ever-increasing acidity gradient could prove thermodynamically difficult. There is also evidence that the integrity of the cell membrane lipid bilayer is compromised by acidity at a pH of 3 and below (61,62), which could promote leakage of phagolysosomal contents into the cytoplasm with damage to the host cell. Consequently, we propose that a larger variation in macrophage phagolysosomal pH acts as a diversified bet-hedging strategy against the stochasticity of the potential pH tolerances of ingested microbes within the physiological limits of achievable acidification.…”

Effects of Short-Term Alkaline Adaptation on Surface Properties of Listeria monocytogenes 10403S

“…monocytogenes is known to display an adaptive response in which exposure to non lethal environmental stress, enables it to more effectively survive subsequent [more severe] challenges by the same or different environmental stress(es) [8][9][10][11][12]. Such adaptation has been noted in response to alkali stress [13][14][15][16][17], and has also been reported to confer cross protection against subsequent thermal stress, ethanol and alcohol stress [4,11,18].Alkali conditions can induce the solubilisation of bacterial surface proteins [19,20], resulting in exposure of hydrophobic sites of adjacent lipids to the extracellular environment [21]. Alkali may also directly attack the structure of the cell membrane by saponification of membrane lipids or alteration of the membrane fatty acids ratio [22,23] Considerable information is available about the general structure and biochemistry of the surface of L. monocytogenes, although less is known about the direct physical effects of environmental stresses and in particular alkali stress, on these structures and processes.…”

Apolipophorin III interaction with model membranes composed of phosphatidylcholine and sphingomyelin using differential scanning calorimetry

“…Upon rehydration of SM and DMPC in buffer, MLVs are formed [30, 31]. As discussed in detail previously, rehydrated dispersions of pure DMPC when not extensively annealed at low temperatures exhibit two endothermic events [32].…”