title: Meperidine suppresses the excitability of spinal dorsal horn neurons.
abstract: BACKGROUND
  In addition to local anesthetics, meperidine has been successfully used for local anesthesia. When applied intrathecally, the dorsal horn neurons of the superficial laminae are exposed to high concentrations of meperidine. These cells represent an important point for the transmission of pain information. This study investigated the blocking effects of meperidine on different ionic currents of spinal dorsal horn neurons and, in particular, its impact on the generation of action potentials.
  
  
  METHODS
  Using a combination of the patch clamp technique and the entire soma isolation method, the action of meperidine on voltage-gated Na+ and K+ currents in spinal dorsal horn neurons of rats was described. Current clamp recordings from intact neurons showed the functional relevance of the ion current blockade for the generation of action potentials.
  
  
  RESULTS
  Externally applied meperidine reversibly blocked voltage-gated Na+ currents with a half-maximum inhibiting concentration (IC50) of 112 microM. During repetitive stimulation, a slight phasic block occurred. In addition, A-type K+ currents and delayed-rectifier K+ currents were affected in a dose-dependent manner, with IC50 values of 102 and 52 microM, respectively. In the current clamp mode, single action potentials were suppressed by meperidine. The firing frequency was lowered to 54% at concentrations (100 microM) insufficient for the suppression of a single action potential.
  
  
  CONCLUSIONS
  Meperidine inhibits the complex mechanism of generating action potentials in spinal dorsal horn neurons by the blockade of voltage-gated Na+ and K+ channels. This can contribute to the local anesthetic effect of meperidine during spinal anesthesia.
authors.affiliation: Department of Anesthesiology, Intensive Care Medicine, Pain Therapy, Justus-Liebig-University, Giessen, Germany. matthias.wolff@physiologie.med.uni-giessen.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Wolff
authors.forename: Andrea
authors.initials: A
authors.lastname: Olschewski
authors.forename: Werner
authors.initials: W
authors.lastname: Vogel
authors.forename: Gunter
authors.initials: G
authors.lastname: Hempelmann
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D004305:Dose-Response Relationship, Drug; D008614:Meperidine / Q000494:pharmacology*; D020671:Posterior Horn Cells / Q000187:drug effects* / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects; D051381:Rats; D015222:Sodium Channels / Q000187:drug effects
chemical_list: D015221:Potassium Channels; D015222:Sodium Channels; D008614:Meperidine