The transient receptor potential A1 (TRPA1) channel is the molecular target for environmental irritants and pungent chemicals, such as cinnamaldehyde and mustard oil. Extracellular Ca(2+) is a key regulator of TRPA1 activity, both potentiating and subsequently inactivating it. In this report, we provide evidence that the effect of extracellular Ca(2+) on these processes is indirect and can be entirely attributed to entry through TRPA1 and subsequent elevation of intracellular calcium. Specifically, we found that in a pore mutant of TRPA1, D918A, in which Ca(2+) permeability was greatly reduced, extracellular Ca(2+) produced neither potentiation nor inactivation. Both processes were restored by reducing intracellular Ca(2+) buffering, which allowed intracellular Ca(2+) levels to become elevated upon entry through D918A channels. Application of Ca(2+) to the cytosolic face of excised patches was sufficient to produce both potentiation and inactivation of TRPA1 channels. Moreover, in whole cell recordings, elevation of intracellular Ca(2+) by UV uncaging of 1-(4,5-dimethoxy-2-nitrophenyl)-EDTA-potentiated TRPA1 currents. In addition, our data show that potentiation and inactivation are independent processes. TRPA1 currents could be inactivated by Mg(2+), Ba(2+), and Ca(2+) but potentiated only by Ba(2+) and Ca(2+). Saturating activation by cinnamaldehyde or mustard oil occluded potentiation but did not interfere with inactivation. Last, neither process was affected by mutation of a putative intracellular Ca(2+)-binding EF-hand motif. In conclusion, we have further clarified the mechanisms of potentiation and inactivation of TRPA1 using the D918A pore mutant, an important tool for investigating the contribution of Ca(2+) influx through TRPA1 to nociceptive signaling.