title: Local anaesthetics inhibit signalling of human NMDA receptors recombinantly expressed in Xenopus laevis oocytes: role of protein kinase C.
abstract: BACKGROUND
  N-methyl-D-aspartate (NMDA)-receptor activation contributes to postoperative hyperalgesia. Studies in volunteers have shown that intravenous local anaesthetics (LAs) prevent the development of hyperalgesic pain states. One potential explanation for this beneficial effect is the inhibition of NMDA receptor activation. Therefore, we studied the effects of LA on NMDA receptor function.
  
  
  METHODS
  The human NR1A/NR2A NMDA receptor was expressed recombinantly in Xenopus laevis oocytes. Peak currents were measured by voltage clamp in Mg- and Ca2+-free, Ba2+-containing Tyrode's solution. Holding potential was -70 mV. Oocytes were stimulated with glutamate/glycine (at EC50) with or without 10 min prior incubation in bupivacaine, levobupivacaine, S-(-)-ropivacaine, or lidocaine (all at 10(-9)-10(-4) M), procaine (10(-4) M), R-(+)-ropivacaine (10(-4) M), QX314 (permanently charged, 5 x 10(-4) M) extracellularly or intracellularly or benzocaine (permanently uncharged, 5 x 10(-3) M). We also determined the effect of the protein kinase C (PKC) inhibitors chelerythrine (5 x 10(-5) M), calphostin C (3 x 10(-6) M) and Ro 31-8220 (10(-7) M), and the effect of PKC activation with phorbolester (10(-6) M).
  
  
  RESULTS
  Non-injected oocytes were unresponsive to agonist application, but oocytes expressing NMDA receptors responded with inward currents (1.1+/-0.08 microA). All LA concentration-dependently inhibited agonist responses. The inhibition was reversible and stereoselective. Intracellular QX314 reduced responses to 59% of control, but extracellular QX314 was without effect. Benzocaine reduced responses to 33% of control. PKC inhibitors had no additional inhibitory effect beyond that of bupivacaine. The effect of PKC activation was abolished in the presence of bupivacaine.
  
  
  CONCLUSIONS
  All LA tested inhibited the activation of human NMDA receptors in a concentration dependent fashion. This effect may contribute to reduced hyperalgesia and opiate tolerance observed after systemic administration of LA. The effect is independent of the charge of LA; site of action is intracellular. The mechanism of action may be mediated by inhibition of PKC.
authors.affiliation: Department of Anaesthesiology and Intensive Care, University Hospital, Münster, Germany. hahnenkamp@anit.uni-muenster.de
authors.forename: K
authors.initials: K
authors.lastname: Hahnenkamp
authors.forename: M E
authors.initials: ME
authors.lastname: Durieux
authors.forename: A
authors.initials: A
authors.lastname: Hahnenkamp
authors.forename: S K
authors.initials: SK
authors.lastname: Schauerte
authors.forename: C W
authors.initials: CW
authors.lastname: Hoenemann
authors.forename: V
authors.initials: V
authors.lastname: Vegh
authors.forename: G
authors.initials: G
authors.lastname: Theilmeier
authors.forename: M W
authors.initials: MW
authors.lastname: Hollmann
mesh_terms: D000779:Anesthetics, Local / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques / Q000379:methods; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects* / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014982:Xenopus laevis
chemical_list: D000779:Anesthetics, Local; D004791:Enzyme Inhibitors; D016194:Receptors, N-Methyl-D-Aspartate; D011994:Recombinant Proteins; D011493:Protein Kinase C