Fig. 2. Irritant volatile anesthetics activate transient receptor potential (TRP)-A1 expressed in peripheral nociceptors. (A ) Typical traces of fura-2-fluorescence ratios representing changes in intracellular calcium concentration [Ca2+]iinduced by desflurane (des, 1.15 mm–2 MAC), allyl-isothiocyanate (aitc, 100 μm), and capsaicin (cap, 1 μm) in dorsal root ganglion (DRG) neurons isolated and cultured from TRPA1 wild-type mice. Application of desflurane, mustard oil, and capsaicin is indicated by horizontal lines. Two cells respond to all the three substances, one cell only to capsaicin (bold black trace ), and two cells do not respond to any of the stimuli (dashed traces ). (B ) Representative traces of changes in [Ca2+]iin response to desflurane, mustard oil, and capsaicin in DRG neurons isolated and cultured from TRPA1 knock-out mice. Labeling of the traces is similar to that described for (A ). (C ) Quantitative analysis of responses to desflurane in DRG neurons from TRPA1 wild-type (trpa1 +/+) and knock-out (trpa1 −/−) mice. A total of 35.5% of wild-type cells responded to desflurane but only 3% of cells isolated from knock-out mice responded (n = 28 [trpa1 +/+] and n = 42 [trpa1 −/−]). (D ) Representative traces of changes in [Ca2+]iin response to isoflurane, mustard oil, and capsaicin in DRG neurons from TRPA1 wild-type mice. Experimental setup and labeling of traces is similar to (A ) but isoflurane (iso) was used instead of desflurane.