Fig. 5

M572 residue in TRPV1 S4-S5 linker region mediates the effect of 1,4-dioxane and its analogs. a Structures of 1,3-dioxane, tetrahydrofuran, and 1,3,5-trioxane compared with that of 1,4-dioxane. b Activation of TRPV1 by 1,4-dioxane analogs. Representative trace of TRPV1 whole-cell currents from TRPV1-expressing HEK293 cells evoked by 1,4-dioxane (2%), 1,3-dioxane (2%), 1,3,5-trioxane (2%), tetrahydrofuran (THF, 2%), and capsaicin (Cap, 1 μM) at −60 mV. c Concentration-response curves of whole-cell TRPV1 currents evoked by 1,3-dioxane and tetrahydrofuran, respectively. d Representative whole-cell recording from TRPV2-expressing HEK293 cell showing its responses to 2-APB and insensitivity to 1,4-dioxane. e Top, putative membrane topology of a single TRPV1 subunit. Bottom, amino acid alignment of the linker of S4-S5 between TRPV1 and TRPV2, with the identical residues shaded in black. f Representative whole-cell recordings showing that 1,4-dioxane failed to activate V1/V2(L4-5) chimeric channel, which is a TRPV1 mutant with the linker for S4-S5 swapped by the cognate segment of rat TRPV2; however, the response to capsaicin (Cap) was retained. g Summary data of current densities at −60 mV evoked by capsaicin and 1,4-dioxane obtained by whole-cell recordings. Rat TRPV1 mutants with the N terminus (Nt), linker S2-S3 (L1-2), linker S2-S3 (L2-3), linker S2-S3 (L3-4), linker S4-S5 (L4-5), linker S5-S6 (L5-6), and the C terminus (Ct) swapped by the cognate segments of rat TRPV2, respectively. h Representative whole-cell recordings showing that mutant channel V1(M572V) lost sensitivity to 1,4-dioxane, though the response to capsaicin was retained. i Average responses of the mutant channels evoked by different stimuli as indicated. Residues in the linker S4-S5 of TRPV1 were individually mutated to the corresponding residues of TRPV2. Whole-cell currents were recorded from transiently transfected HEK293 cells at −60 mV, and current densities were determined by dividing the peak current amplitudes by membrane capacitance. j Whole-cell recordings were made at −60 mV from HEK293 cells showing that 1,4-dioxane (2%), 1,3-dioxane (2%), and tetrahydrofuran (2%) failed to activate V1(M572V), while the response to capsaicin (1 μM) was retained. k Summary data of current densities at −60 mV evoked by capsaicin (1 μM), 1,4-dioxane (2%), 1,3-dioxane (2%), and 1,3,5-trioxane (2%) and tetrahydrofuran (2%) obtained by whole-cell recordings