Abrupt modifications of phospholipid bilayer properties at critical cholesterol concentrations

Abstract

The fluorescence generalized polarization (GP) of 2-dimethylamino-6-lauroylnaphthalene (Laurdan) reveals different effects of cholesterol on the phase behavior of phospholipid bilayers. Phospholipid vesicles composed of gel, liquid-crystalline, and coexisting domains of the two phases have been studied at temperatures from 1 to 65 degrees C, without cholesterol and with cholesterol concentrations of 3-50 mol %. Laurdan GP measurements show the general effect of cholesterol of increasing the molecular dynamics of the gel and of decreasing the molecular dynamics of the liquid-crystalline phase. In the liquid-crystalline phase, the increased order yields Laurdan GP values close to those obtained in the gel phase. At cholesterol concentrations > 15 mol % a phase transition cannot be detected. Using the wavelength dependence of the excitation and emission GP spectra we determine that differences between the two phospholipid phases cannot be detected. In particular, in vesicles composed of coexisting gel and liquid-crystalline phases the GP wavelength dependence characteristic of coexisting domains cannot be observed at cholesterol concentrations > or = 15 mol %. Cholesterol causes the decrease in both the polarity and the dipolar relaxation effects on the neighborhood of the fluorescent naphthalene moiety of Laurdan. Probably because of a cholesterol-induced increase in the bilayer packing, these effects do not occur continuously with the increase of cholesterol concentration in the bilayer. Cholesterol concentrations inducing higher Laurdan GP values have been determined at about 5, 10, 15, 30, and 45 mol % with respect to phospholipids. We propose that the formation of ordered molecular microdomains at critical cholesterol concentrations can explain the occurrence of the observed discontinuities.

Induction of Highly Curved Structures in Relation to Membrane Permeabilization and Budding by the Triterpenoid Saponins, α- and δ-Hederin

“…8, C and D) in accordance with other studies (49,50). We observed a slight reduction of GP ex values at low temperatures that became important at physiological temperatures (Fig.…”

Cholesterol facilitates the native mechanism of Ca2+-triggered membrane fusion

“…In order to fully recover both the ability of CVs to fuse and the efficiency of fusion, both recovery of native cholesterol levels and reformation of appropriate cholesterol-rich microdomains appear to be necessary. The spontaneous recovery of the Ca 2+ sensitivity and kinetics of fusion after full recovery of the native CV membrane cholesterol level is consistent with a critical total cholesterol concentration required to support formation of rafts (Parasassi et al, 1995). Additionally, model membrane studies show that increasing cholesterol concentration in lipid bilayers results in a decreased transition temperature to the liquid ordered phase (Parasassi et al, 1995;Filippov et al, 2003).…”

“…The spontaneous recovery of the Ca 2+ sensitivity and kinetics of fusion after full recovery of the native CV membrane cholesterol level is consistent with a critical total cholesterol concentration required to support formation of rafts (Parasassi et al, 1995). Additionally, model membrane studies show that increasing cholesterol concentration in lipid bilayers results in a decreased transition temperature to the liquid ordered phase (Parasassi et al, 1995;Filippov et al, 2003). Thus, at a fixed temperature, varying the cholesterol concentration in membranes identifies a critical concentration of cholesterol for the 'spontaneous' transition to the liquid ordered phase.…”

Effect of acetylsalicylic acid on the current–voltage characteristics of planar lipid membranes

“…Lipid bilayers containing cholesterol may also exhibit phase separation into cholesterol-rich (liquid-ordered) and cholesterol-poor (liquid disordered) domains with the increase of cholesterol content [11,[19][20][21][22][23][24], although the molecular organization of such cholesterol-containing bilayers is still a matter of debate, as is the significance of the structures like lipid rafts and hexagonal superlattices [25][26][27][28][29]. With the increasing fraction of cholesterol, the BLM became more stable at the beginning, and the threshold voltage of bilayer breakdown (rupture) was initially increased.…”