Exceptionally high thermal sensitivity of rattlesnake TRPA1 correlates with peak current amplitude.

Extraordinary infrared-sensing ability of snake pit organs closely correlates with rich expression of TRPA1 transcripts in pit-innervating sensory neurons, strongly suggesting that TRPA1 is the molecular basis of the infrared detection. Here, it is shown that temperature coefficient Q10 (the fold current increase over 10°C increase) of rattlesnake TRPA1 heterologously expressed in Xenopus oocytes increases proportionally to current amplitudes when appraised with two independent methods, the canonical Arrhenius plot analysis and newly devised Q10 scanning that assigns Q10 to each recorded temperature point. Moreover, for larger TRPA1 currents, the rise of Q10 from elevation of current sizes was steeper, yielding maximal Q10s up to ~100,000. TRPA1 from boas with less sensitive infrared-sensing ability was also sharply activated by temperature increase in oocytes, while Q10 rise from escalating current amplitudes was moderate compared to rattlesnake TRPA1. In contrast, thermal sensitivity of Drosophila TRPA1 was little dependent on current sizes, indicating that the steeply proportional current amplitude/thermosensitivity relationship is unique to the snake TRPA1s. Taken together, rattlesnake and boa TRPA1s are regulated to generate sufficient thermal sensitivity for infrared detection, providing an interesting context to further study the temperature-dependent activation mechanism of thermo-TRPs.