The effects of ropivacaine on sodium currents in dorsal horn neurons of neonatal rats.
We used a whole cell patch clamp technique to study the effects of ropivacaine on rat dorsal horn neurons. Under voltage clamp, ropivacaine (10-400 microM) produced a dose-dependent inhibition of sodium current. From a holding potential (V(h)) of -80 mV, sodium currents evoked by test pulses to 0 mV were inhibited by ropivacaine with a mean drug concentration required to produce 50% current inhibition (IC(50)) value of 117.3 microM, which was more than the value of the bupivacaine (IC(50) 53.7 microM). The inhibition effect of ropivacaine was also voltage-dependent. Current evoked from a V(h) of -60 mV was inhibited by ropivacaine with a mean IC(50) value of 74.3 microM, which was less than that obtained at the V(h) of -80 mV. The inhibition effect of ropivacaine on sodium current was use dependent. Repeated activation by a train of depolarizing pulses (5 Hz, 20 ms) increased the inhibitory effects of ropivacaine. The ratio amplitudes of the 20th to the first pulse were 91.2% and 71.1%, respectively, in the absence and presence of ropivacaine (50 microM). Ropivacaine also produced a significant hyperpolarizing shift of 11 mV in the steady-state inactivation curve of sodium current. The inhibition of ropivacaine on the sodium channel may contribute to the mechanism of action of local anesthetics during epidural and spinal anesthesia.
Liu
B G
BG
Department of Anesthesiology, Shanghai First People's Hospital, Shanghai Medical University, Shanghai, China. liubaogang@mailcity.com
Zhuang
X L
XL
Li
S T
ST
Xu
G H
GH
D000577:Amides / Q000494:pharmacology*; D000779:Anesthetics, Local / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D066298:In Vitro Techniques; D018408:Patch-Clamp Techniques; D020671:Posterior Horn Cells / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D000077212:Ropivacaine; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*
D000577:Amides; D000779:Anesthetics, Local; D015222:Sodium Channels; D000077212:Ropivacaine