British Journal of Anaesthesia, 2000, Vol. 85, No. 5 740-746
© 2000 The Board of Management and Trustees of the British Journal of Anaesthesia
Interaction of local anaesthetics with recombinant µ, 
, and 
-opioid receptors expressed in Chinese hamster ovary cells
1University Department of Anaesthesia, Leicester Royal Infirmary, Leicester, LE1 5WW, UK. 2Oregon Health Sciences University, Portland, OR, USA
Local anaesthetics potentiate epidural or intrathecal opioid analgesia via a poorly defined mechanism. In this study, we have examined the interaction of local anaesthetics (lidocaine, bupivacaine and its optical isomers, tetracaine, procaine and prilocaine) with recombinant µ-, 
-, and 
-opioid receptors expressed in Chinese hamster ovary cells (CHO-µ, , and , respectively). Lidocaine produced a concentration-dependent displacement of radiolabelled opioid antagonist [3H]diprenorphine ([3H]DPN) binding with the following rank order of inhibitor constant (Ki): (210 µM) > µ (552 µM) > (1810 µM). Procaine, prilocaine, tetracaine and bupivacaine also displaced [3H]DPN binding in CHO- µ with Ki values of 244, 204, 43 and 161 µM respectively. Lidocaine produced a concentration-dependent and naloxone-insensitive inhibition of cAMP formation in all cell lines including untransfected cells. Concentration producing 50% inhibition of maximum was µ, 1.32 mM; , 2.41 mM; , 1.27 mM; untransfected, 2.78 mM. When lidocaine (300 µM) was co-incubated with spiradoline (-selective) and [D-Ala2, MePhe4, Gly(ol)5] enkephalin (DAMGO µ-selective) in CHO- and µ cells we did not observe an additive interaction for cAMP formation. In contrast, there was an apparent inhibitory action of the combination at the receptor. This study suggests that clinical concentrations of local anaesthetics interact with µ and but not opioid receptors. As there was no synergism between local anaesthetics and opioids we suggest that the interaction of these agents in the clinical setting does not occur at the cellular level.
Br J Anaesth 2000; 85: 740–6
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