Abstract

By responding to stimuli of diverse physics and chemical nature, transient receptor potential (TRP) channels fulfill important physiological functions in both excitable and non-excitable cells. Capsaicin (CAP) from chili peppers and allyl isothiocyanate (AITC) from mustard are natural and potent agonists for TRPV1 and TRPA1, respectively. Upon exposure to hydrogen peroxide (H 2 O 2 ), the central molecule in redox signaling pathways, TRPA1 shows robust activation and much higher sensitivity than TRPV1. Singlet oxygen ( 1 O 2 ), the molecular oxygen in electrically excited states, is the least studied reactive oxygen species (ROS). Here we report that both TRPV1 and TRPA1 are sensitive to the modification by 1 O 2 , but they exhibit drastically different responses. 1 O 2 generated by excited photosensitizers enhances the function of TRPV1 by accelerating its opening kinetics, increasing the current amplitude, and left-shifting the voltage-dependent activation curve towards physiological membrane potentials. A histidine residue located in the N-terminal ankyrin repeat domain of TRPV1 is identified to be important in 1 O 2 modification process. In contrast, as reported by imaging of cytosolic calcium, 1 O 2 modification of TRPA1 leads to a transient increase and then permanent inhibition of channel activity, and eventually obliterates TRPA1's response to AITC but not carvacrol – electrophilic and non-electrophilic agonists for TRPA1, respectively. Conversely, hTRPA1 is much more sensitive to H 2 O 2 , with the EC50 for channel activation about five times lower than that of hTRPV1, and the responses by two channels to H 2 O 2 mainly involves intracellular cysteine residues. The physiological significance of the distinct responses of TRPV1 and TRPA1 to two representative ROS, 1 O 2 and H 2 O 2 , warrants further investigation.