EFFECTS OF INTRAVENOUS ANESTHETICS ON NERVE AXONS

The effects of ketamine, etomidate, alphaxalone and alphadolone acetat e on nodal sodium and potassium currents of frog myelinated nerve fibr e have been examined. The four general anaesthetics reversibly depress ed ionic currents, although they tended to be more effective in blocki ng potassium than sodium current. The potassium current was reduced by etomidate and alphaxalone in a time-dependent manner. This was not fo und for ketamine and alphadolone acetate. In addition to blocking effe cts on sodium current, etomidate, alphaxalone and alphadolone acetate, but not ketamine, induced a negative shift of steady-state sodium ina ctivation-voltage curves. Collectively, the general anaesthetics appea red to alter specifically and differentially sodium and potassium chan nel-gating systems. The simplest interpretation of these results sugge sts that the compounds produce state-dependent blocks of ionic channel s, and that there are general anaesthetic receptor sites located on th e channel proteins themselves. Furthermore, potassium and sodium chann els may contain several types of receptor sites, through which anaesth etics could exert their different actions.