Perturbation effect of local anaesthetics on synaptosomes: variation with depth of the spin label probe

Stearic acids labeled with a doxyl group at the 5th, 12th and 16th carbon positions were used as the spin probes for an investigation of the perturbation effects of two local anaesthetics (the 2-piperidinoethylester of phenyl carbamic acid and the piperidinoethylester of 2-heptyloxyphenylcarbamic acid) on rat brain synaptosomes. For a quantitation of the perturbation effects we have studied the order parameter S of the spin probe, incorporated in the membrane, calculated from the ESR spectra as a function of temperature and concentration of local anaesthetics. The local anaesthetics had a different disordering efficiency at different depths of the membrane. It follows from our results that the perturbing effects of the anaesthetics increase relative to the depth of the membrane, and the extent of perturbation correlates with local anaesthetic activity.