Abstract: AIM: To study the interactions of propo-fol and midazolam on the whole-cell sodium channel cur-rents in rat sympathetic ganglion neurons.METHODS: Whole-cell patch-clamp recordings were made from enzy-matically isolated rat (7-10 d)superior cervical sympa-thetic ganglion neurons.Isobolographic analysis was ap-plied to evaluate the potency of combinations of propofol and midazolam on Na⁺channel currents.RESULTS: Under V_h = 80 mV and V_t =0 mV. Propofol and mida-zolam dose-dependently blocked Na⁺ currents with a mean drug concentration required to produce 50%current inhibition(IC₅₀ ):33.12 μmol·L^-1 and18.35 μmol·L^-1; clinically relevant concentrations of propofol and midazo-lam reduced Na⁺ peak currents by 27.66%(P <0.01) and 19.88%(P <0.05).The IC₅₀ values of midazolam combined with 1/4 and 3/4 IC₅₀ propofol located in the 95% confidence limits of theoretical additive line; the IC₅₀ values of midazolam combined with 1/2 IC₅₀ propofol located under the 95%confidence limitsof theoretical ad-ditive line. CONCLUSION: Clinically relevant concen-trations of propofol and midazolam have direct and dose-dependent inhibition on the Na⁺ channel currents of rat sympathetic ganglion neurons.The interactions between propofol and midazolam at Na⁺ channel current are addi-tive, in addition to the synergism which equi-effective doses are used.Reduction of cardiovascular depression during co-inductionof propofol and midazolam may be rel-evant to the reduction of doses.

Key words: anesthesia, propofol, midazolam, sym-pathetic ganglion, patch-clamp/sodium channel, drng in-teraction