Abstract
1 Mammalian transient receptor potential (TRP) channels include the nonselective cation channel TRPV1, which is activated by a range of stimuli including low pH, vanilloids and heat. Previously, selective mutagenesis experiments identified an intracellular residue (S512Y) critical to discriminating between pH and vanilloid (capsaicin) gating of the rat TRPV1 receptor. 2 In this study, switching the equivalent residue in the human TRPV1 (which has some significant differences with the rat TRPV1) also rendered this channel relatively insensitive to activation by capsaicin and proved critical in determining the receptor's sensitivity to the putative endovanilloid N-arachidonoyl-dopamine (NADA), suggesting a similar mode of activation for these two agonists. 3 Potency of pH gating was reduced; however, voltage-dependent outward rectification properties of the pH-dependent current and gating by heat and pH sensitisation of the S512Y heat response remained unaffected. 4 Surprisingly, residual capsaicin gating was detected and could be sensitised by pH even in the presence of a competitive antagonist. Taken together, these findings indicate that effective functional interaction of capsaicin with the S512Y channel still occurred, although the vanilloid-dependent gating per se was severely compromised. 5 This observation provides additional evidence for capsaicin interacting at multiple sites, distinct from the S512 residue located close to the intracellular face of the pore.