Depolarizing effect of various local anaesthetics on the Helix aspersa neurons: dose-response relationship

The depolarizing effect of various local anaesthetics (LA) on the membrane potential of Helix central neurons has been examined. There is a relation between depolarizing effect and concentration of LA in the bath that is linear over a range of concentrations. The slope of the curve is significantly higher for amethocaine (tetracaine) than for procaine while for dibucaine the dose-response relation is not linear. The blockade of a response to acetylcholine (ACh) is about two fold higher for dibucaine and amethocaine than for procaine. These results suggest that both amethocaine and procaine act at the ACh-site in addition to their binding with specific sites located within the ionic channel lumen; dibucaine appears to act through another mechanism.