Effect of anesthetics on membrane fluidity tested by two different techniques: EPR spin labels and polarization of perylene fluorescence.

We have investigated the effect of n-butanol on the spectroscopic properties of two types of probes, that are usually employed to detect membrane fluidity, in mitochondrial phospholipid vesicles and mitochondrial membranes. Although both a spin label (16-doxylstearate) and the fluorescent probe perylene detect a higher immobilization of the membrane in comparison with phospholipid vesicles, the effect of butanol in the case of the membrane is strikingly different with the two techniques employed, showing increased fluidity in the case of the spin label and decreased fluidity with the fluorescent probe.