Abstract: AIM: To compare the blocking effect of ropivacaine and bupivacaine on sodium channels of rat dosal root ganglia(DRG) using whole cell recording tech-nique.METHODS: Rat DRG neuronswere enzymatical-ly isolated, tetrodotoxin-sensitive(TTX-s) and tetrodotox-in-resistant (TTX-r) sodium currents of DRGwere record-ed by whole cell recording.Drugs were given in bath solu-tion.The concentrations of ropivacaine were 10, 30, 100, 1 000 μmol·L^-1 and bupivacaine were 10, 30, 100, 300 μmol·L^-1.The recording number in each dose groupwas six.RESULTS: CsCl in extracellular fluid and TEA in intracellular fluid were used to block the potassium chan-nels.Sodium currentswere recordedwhen the holding po-tential was -70 mV and a serials of pulse with step 10 mV and duration 70 mswas given.TTX-s sodium channel was recorded in 80.1%large DRG cells and TTX-r sodi-um channel was recorded in 92.4% medium and small DRG cells, of which 56.3% cells had no response to 1 μmol·L^-1 TTX.The half-maximal blocking concentra-tions of ropivacaine on TTX-r sodium channel was 65.7± 6.1 μmol·L^-1, which wasmuch lower than that on TTX-s sodium channel 246.8±11.2 μmol·L^-1 (P<0.01); The half-maximal blocking concentrations of bupivacaine on TTX-r and TTX-s sodium channel was essentially the same (27.2±6.2 μmol·L^-1 vs 29.5±2.9 μmol·L^-1, P >0.05).CONCLUSION: Ropivacaine preferentially blocks TTX-r sodium channel.Selective blocking of TTX-r and TTX-s sodium channel was one of the reasons of se-peration of sensation and motion when it is used in epi-dural anesthesia.

Key words: ropivacaine, bupivacaine, patch clamp technique, sodium channel, dosal root ganglia