[Use of excimerization of pyrene for assessing lipid microviscosity in biological membranes]

A method for estimating the fluidity of natural membranes from the pyrene excimer/monomer fluorescence ratio (Ie/Im) is proposed. The method makes it possible to exclude artefacts such as fluorescence quenching, aggregation, and redistribution of the probe in lipid mains with different microviscosity. It is shown that, upon variation of intramembrane pyrene concentration [pyr], the occurrence of a common crossover point in pyrene fluorescence spectra normalized to the corresponding probe concentration (isoemission or isobestic point) or, as a consequence, the linear dependence of Ie/[pyr] on Im/[pyr] can serve as a criterion of diffusion (fluidity)-controlled excimerization of pyrene. The isobestic point can be used for determining the range of working concentrations of the probe in membrane suspension. It was found from the intensity of pyrene fluorescence in the isobestic point and quenching with potassium iodide that at t < 30 degrees C, the probe is uniformly distributed throughout the membrane, and its excimerization is mainly controlled by the microviscosity of environment.