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. The se ligand-gated ion channels are also sensitive to low pH, elevated tempera ture and the endocannabinoid, anandamide. In this study, we have measured c apsaicin- and anandamide-induced elevations in intracellular calcium concen trations ([Ca2+](i)) in fura-2 loaded HEK293 cells stably expressing the ra t VR1 receptor at 22, 37 and 50 degreesC. Both capsaicin and anandamide pro duced a concentration-dependent elevation in [Ca2+](i) at all temperatures. pEC(50) values were 7.74 and 5.69 at 22 degreesC and 6.90 and 5.15 at 37 d egreesC for capsaicin and anandamide, respectively. At 50 degreesC, the pEC (50) value for capsaicin was 6.36 but the response to anandamide did not sa turate. Responses to both agonists were sensitive to ruthenium red and caps azepine at all temperatures. This temperature-dependent reduction in potenc y may result from desensitization. (C) 2001 Published by Elsevier Science B .V.