Abstract: AIM: To explore the influence of different concentration midazolam on the macroscopic voltage-gated potassium currents and to discuss the relationship between potassium currents andinhibitory effect of clinical relevant concentration midazolam on sympathetic nervous system.METHODS: Superior sympathetic ganglion neurons were dissociated enzymatically from 7 to10-day-old rat.Experiments were performed about 5 h after plating atroom temperature (20-24 ℃).Appropriate solution was chosen to separate the K⁺ current from the other transmembrane currents.1 μmol·L^-1 TTX was applied to the extracelluar solution to block the Na + current.Midazolam was also resolvedin extracelluar solution to get various concentration (0.1, 0.3, 3, 10, 50, 100 μmol·L^-1).Currents were recorded with the patch-clamp technique in whole cell configuration using glass electrodes with a tip resistance of 2-4 M.Potassium currents were evoked by test pulse from^-100 mV to +30 mV with holding potential-80mV. Data were analyzed using Clampfit 6.0 and Oringih 5.0 software.Whole-cell current records were corrected for leakage and capacitance by using the P/5 protocol.RESULTS: Midazolam dose-dependently inhibited the wholecell potassium currents.Clinical relevant concentrationmidazolam (0.3 μmol·L^-1) only reduced the peak currents by 3.89 %(P =0.88).The concentration required to produce 50 %current inhibition(IC₅₀) was 76.065 μmol·L^-1.CONCLUSION: Midazolam inhibits the whole-cell potassium current significantly and dose-dependently, but clinical relevant concentration midazolam has minor effect on the potassium currents, indicating that the inhibitory effect of midazolam on potassium current is not related to the suppression of activity of sympathetic system.

Key words: midazolam, superior cervical ganglion, potassium current