The effects of local and intravenous anesthetics on recombinant rat VR1 vanilloid receptors.

Unlabelled: Capsaicin, acting at the vanilloid 1 receptor (VR1), may potentiate local anesthetic activity, and as a ligand-gated ion channel of the transient receptor potential family, may also be a target for IV general anesthetics. We have examined whether local (lidocaine, prilocaine, and procaine 0.1-10 mM; 10 mM represents 0.25%-0.27% wt/vol) or IV anesthetics (propofol 10 micro M, thiopental 100 micro M, and ketamine 100 micro M) interact with recombinant rat VR1 expressed in human embryonic kidney (HEK293) cells (VR1-HEK293). We have assessed receptor interaction functionally by monitoring intracellular Ca(2+) ([Ca(2+)](i)) in Fura2-loaded cells at 37 degrees C. The addition of capsaicin (60 nM) produced a time-dependent biphasic increase in [Ca(2+)](i) amounting to 50-100 nM above than basal, which was inhibited by capsazepine 10 micro M and was absent in wild type HEK293 cells. Lidocaine and prilocaine alone (e.g., at 10 mM) significantly increased [Ca(2+)](i) by 67 +/- 6 nM and 33 +/- 7 nM, respectively, and concentration-dependently inhibited the capsaicin response. The effects of procaine were obscured by anesthetic-induced quenching of Fura2. In wild type HEK293 cells, lidocaine (10 mM) alone produced a small increase in [Ca(2+)](i). All IV anesthetics failed to modify capsaicin-increased [Ca(2+)](i). In conclusion, the present data suggest that local but not IV general anesthetics interact with recombinant rat VR1 receptors with the former anesthetics having antagonistic activity.
Implications: Vanilloid receptors (VR1) are activated by capsaicin, the pain-producing component of hot chili peppers. We suggest that local (but not IV general) anesthetics may have inhibitory actions on this receptor.