title: Blockade of Na+ and K+ currents by local anesthetics in the dorsal horn neurons of the spinal cord.
abstract: BACKGROUND
  The dorsal horn of the spinal cord is a pivotal point for transmission of neuronal pain. During spinal and epidural anesthesia, the neurons of the dorsal horn are exposed to local anesthetics. Unfortunately, little is known about the action of local anesthetics on the major ionic conductances in dorsal horn neurons. In this article, the authors describe the effects of bupivacaine, lidocaine, and mepivacaine on voltage-gated Na+ and K+ currents in the membranes of these neurons.
  
  
  METHODS
  The patch-clamp technique was applied to intact dorsal horn neurons from laminae I-III identified in 200-microm slices of spinal cord from newborn rats. Under voltage-clamp conditions, the whole-cell Na+ and K+ currents activated by depolarization were recorded in the presence of different concentrations of local anesthetics.
  
  
  RESULTS
  Externally applied bupivacaine, lidocaine, and mepivacaine produced tonic block of Na+ currents with different potencies. Half-maximum inhibiting concentrations (IC50) were 26, 112, and 324 microM, respectively. All local anesthetics investigated also showed a phasic, that is, a use-dependent, block of Na+ channels. Rapidly inactivating K+ currents (KA currents) also were sensitive to the blockers with IC50 values for tonic blocks of 109, 163, and 236 microM, respectively. The block of KA currents was not use dependent. In contrast to Na+ and KA currents, delayed-rectifier K+ currents were almost insensitive to the local anesthetics applied.
  
  
  CONCLUSIONS
  In clinically relevant concentrations, local anesthetics block Na+ and KA currents but not delayed-rectifier K+ currents in spinal dorsal horn neurons. The molecular mechanisms of Na+ and K+ channel block by local anesthetics seem to be different. Characterization of these mechanisms could be an important step in understanding the complexity of local anesthetic action during spinal and epidural anesthesia.
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, Justus-Liebig-University, Giessen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Olschewski
authors.forename: G
authors.initials: G
authors.lastname: Hempelmann
authors.forename: W
authors.initials: W
authors.lastname: Vogel
authors.forename: B V
authors.initials: BV
authors.lastname: Safronov
mesh_terms: D000779:Anesthetics, Local / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D066298:In Vitro Techniques; D026902:Potassium Channel Blockers; D051381:Rats; D026941:Sodium Channel Blockers; D013116:Spinal Cord / Q000187:drug effects*
chemical_list: D000779:Anesthetics, Local; D026902:Potassium Channel Blockers; D026941:Sodium Channel Blockers