pH-dependent effects of local anaesthetics in perturbing lipid membranes.

The effects of local anaesthetics lidocaine, benzocaine, carbisocaine and carbisocaine derivatives, KaQ-7 and Ka-O, in perturbing bovine brain lipid membranes or egg lecithin membranes were compared at pH 6.0; 7.0; and 8.0. The electron spin resonance method with stearic acid labeled at carbon position 16 as the spin probe was employed. The perturbation effects of lidocaine and Ka-O were found to increase with increasing pH of the sample, whereas the effect of carbisocaine decreased with increasing pH. The perturbation effects of benzocaine and KaQ-7 were independent of pH. The pH-dependent perturbation effects of the local anaesthetics tested on lipid membrane fairly corresponded with their pH-dependent potency to block nerve action potentials.