Sci. Signal., 20 April 2010
Sensation A Hot Channel
Elizabeth M. Adler
Science Signaling, AAAS, Washington, DC 20005, USA
The western diamondback rattlesnake (Crotalus atrox), like other pit vipers and some nonvenomous snakes (pythons and boas), possesses pit organs that sense infrared radiation, facilitating the detection of prey and predators. The mechanism whereby pit organs detect infrared radiation, however, and the identity of the receptor, remain unclear. Noting that pit organs have a membrane innervated by trigeminal somatosensory nerve fibers, Gracheva et al. compared the transcriptomes of rattlesnake trigeminal ganglia (TGs) and dorsal root ganglia (DRGs) and found that a gene encoding an ortholog of the TRPA1 [transient receptor potential (TRP) ankyrin-1] ion channel was enriched in TGs, a disparity that was not evident in non–pit snakes. Although heterologously expressed rattlesnake TRPA1 responded to mustard oil (allyl isothiocyanate, AITC), which activates mammalian TRPA1 channels, it was comparatively insensitive to this agent. Rather, rattlesnake TRPA1 was highly sensitive to temperature, with a threshold for activation at about 28°C and responses that increased steeply with increasing temperature; in contrast, human and zebrafish TRPA1 were activated by AITC but not by heat. Pythons and boas, which are evolutionarily ancient compared with pit vipers, are less sensitive to infrared than are pit vipers and have architecturally less complex pit organs; nonetheless, transcriptome profiling showed enriched expression of TRPA1 in TGs of Python regius and Corallus hortulanus compared with their DRGs, and both python and boa TRPA1 channels were activated by heat. Calcium imaging revealed that most python TG neurons were heat sensitive, and patch-clamp analysis revealed heat-evoked currents characteristic of those mediated by TRPA1 channels. The authors thus conclude that snakes sense infrared radiation through radiant heating of the pit organ and the consequent activation of TRPA1.
E. O. Gracheva, N. T. Ingolia, Y. M. Kelly, J. F. Cordero-Morales, G. Hollopeter, A. T. Chesler, E. E. Sánchez, J. C. Perez, J. S. Weissman, D. Julius, Molecular basis of infrared detection by snakes. Nature 464,1006–1011 (2010). [PubMed]
Citation: E. M. Adler, A Hot Channel. Sci. Signal. 3, ec115 (2010).
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