Temperature-dependent activation of recombinant rat vanilloid VR1 receptors expressed in HEK293 cells by capsaicin and anandamide

Capsaicin activates vanilloid (VR1) receptors found on sensory neurons. These ligand-gated ion channels are also sensitive to low pH, elevated temperature and the endocannabinoid, anandamide. In this study, we have measured capsaicin- and anandamide-induced elevations in intracellular calcium concentrations ([Ca 2+] i) in fura-2 loaded HEK293 cells stably expressing the rat VR1 receptor at 22, 37 and 50 °C. Both capsaicin and anandamide produced a concentration-dependent elevation in [Ca 2+] i at all temperatures. pEC 50 values were 7.74 and 5.69 at 22 °C and 6.90 and 5.15 at 37 °C for capsaicin and anandamide, respectively. At 50 °C, the pEC 50 value for capsaicin was 6.36 but the response to anandamide did not saturate. Responses to both agonists were sensitive to ruthenium red and capsazepine at all temperatures. This temperature-dependent reduction in potency may result from desensitization.