Critical density fluctuations in lipid bilayers detected by fluorescence lifetime heterogeneity

Abstract

The heterogeneity of the decay of the fluorescence of transparinaric acid in single-component lipid bilayers at temperatures above their gel/liquid crystalline phase transition is shown to be due to the presence of regions of higher local density and higher acyl chain order than the predominant fluid regions. This conclusion is based on selective excitation behavior and the observation of time-resolved fluorescence anisotropies that increase at long times. The fractional amplitude of the long lifetime component of the fluorescence shows a temperature variation that conforms to conventional descriptions of critical behavior. The critical exponent extracted from this variation is 1.1, close to the value of 1.0 that describes ultrasonic data. We therefore conclude that liquid crystalline lipid bilayers exhibit critical behavior with significant density and order fluctuations. This behavior must be taken into account in the interpretation of fluorescence and other spectroscopic measurements of the properties of bilayers.

Chain length dependence of anomalous swelling in multilamellar lipid vesicles

“…This model is supported by experimental evidence of an anomalous decrease in the elastic modulus close to the main transition [8]. The pseudocriticality of the main transition of multilamellar vesicles of phosphocholines with saturated fatty acid chains has been established through a variety of experiments and computer simulations [9][10][11][12][13][14], and it has also been shown using computer simulations and NMR a e-mail: stine@ruc.dk b e-mail: dorthe@ruc.dk that the pseudocritical behaviour is enhanced with decreasing chain length of the lipids [13,14]. A consequence of the bending renormalization model is therefore that the anomaly should increase with decreasing chain length.…”

Filipin fluorescence quenching by spin-labeled probes: studies in aqueous solution and in a membrane model system

“…The photophysics of parinaric acid in heterogeneous media has been a matter of debate (Sklar et al, 1977;Wolber and Hudson, 1981;Parasassi et al, 1984;James et al, 1987;Ruggiero and Hudson 1989;Mateo et al, 1993), but the following conclusions seem supported by clear experimental evidence. 1) Although the tetraene has a complex decay even in homogeneous media, the longer lifetime component in membranes can be safely assigned to the probe in a gel phase.…”

Quenching interactions and nonexponential decay: tryptophan 138 of bacteriophage T4 lysozyme

“…Fluorescence decay measurements were obtained by time-correlated single-photon counting. Detailed descriptions of the instrumentation and data collection are given elsewhere [12]. The frequencydoubled output of a Spectra Physics 3640 mode-locked Nd:YAG laser was used to pump synchronously a rhodamine 6G dye laser that was cavity dumped at 800 KHz.…”