A Single Natural Variation Determines Cytosolic Ca(2+)-Mediated Hyperthermosensitivity of TRPA1s from Rattlesnakes and Boas

Transient receptor potential ankyrin 1 from rattlesnakes (rsTRPA1) and boas (bTRPA1) was previously proposed to underlie thermo-sensitive infrared sensing based on transcript enrichment in infrared-sensing neurons and hyper-thermosensitivity expressed in Xenopus oocytes. It is unknown how these TRPA1s show thermosensitivities that overwhelm other thermoreceptors, and why rsTRPA1 is more thermosensitive than bTRPA1. Here, we show that snake TRPA1s differentially require Ca(2+) for hyper-thermosensitivity and that predisposition to cytosolic Ca(2+) potentiation correlates with superior thermosensitivity. Extracellularly applied Ca(2+) upshifted the temperature coefficients (Q10s) of both TRPA1s, for which rsTRPA1, but not bTRPA1, requires cytosolic Ca(2+). Intracellular Ca(2+) chelation and substitutive mutations of the conserved cytosolic Ca(2+)-binding domain lowered rsTRPA1 thermosensitivity comparable to that of bTRPA1. Thapsigargin-evoked Ca(2+) or calmodulin little affected rsTRPA1 activity or thermosensitivity, implying the importance of precise spatiotemporal action of Ca(2+). Remarkably, a single rattlesnake-mimicking substitution in the conserved but presumably dormant cytosolic Ca(2+)-binding domain of bTRPA1 substantially enhanced thermosensitivity through cytosolic Ca(2+) like rsTRPA1, indicating the capability of this single site in the determination of both cytosolic Ca(2+) dependence and thermosensitivity. Collectively, these data suggest that Ca(2+) is essential for the hyper-thermosensitivity of these TRPA1s, and cytosolic potentiation by permeating Ca(2+) may contribute to the natural variation of infrared senses between rattlesnakes and boas.