How cold is it? TRPM8 and TRPA1 in the molecular logic of cold sensation.
Recognition of temperature is a critical element of sensory perception and allows us to evaluate both our external and internal environments. In vertebrates, the somatosensory system can discriminate discrete changes in ambient temperature, which activate nerve endings of primary afferent fibers. These thermosensitive nerves can be further segregated into those that detect either innocuous or noxious (painful) temperatures; the latter neurons being nociceptors. We now know that thermosensitive afferents express ion channels of the transient receptor potential (TRP) family that respond at distinct temperature thresholds, thus establishing the molecular basis for thermosensation. Much is known of those channels mediating the perception of noxious heat; however, those proposed to be involved in cool to noxious cold sensation, TRPM8 and TRPA1, have only recently been described. The former channel is a receptor for menthol, and links the sensations provided by this and other cooling compounds to temperature perception. While TRPM8 almost certainly performs a critical role in cold signaling, its part in nociception is still at issue. The latter channel, TRPA1, is activated by the pungent ingredients in mustard and cinnamon, but has also been postulated to mediate our perception of noxious cold temperatures. However, a number of conflicting reports have suggested that the role of this channel in cold sensation needs to be confirmed. Thus, the molecular logic for the perception of cold-evoked pain remains enigmatic. This review is intended to summarize our current understanding of these cold thermoreceptors, as well as address the current controversy regarding TRPA1 and cold signaling.
McKemy
David D
DD
Department of Biological Sciences, Neurobiology Section and School of Dentistry, University of Southern California, 925 West 34th Street, Room 4110, Los Angeles, CA 90089-0641, USA. mckemy@usc.edu
D000818:Animals; D017487:Ankyrins; D015220:Calcium Channels / Q000502:physiology; D003080:Cold Temperature; D009619:Nociceptors / Q000502:physiology; D000074025:TRPA1 Cation Channel; D050052:TRPC Cation Channels; D050053:TRPM Cation Channels / Q000502:physiology*; D013823:Thermoreceptors / Q000502:physiology; D013697:Thermosensing / Q000502:physiology*; D050051:Transient Receptor Potential Channels / Q000502:physiology*
D017487:Ankyrins; D015220:Calcium Channels; D000074025:TRPA1 Cation Channel; D050052:TRPC Cation Channels; D050053:TRPM Cation Channels; C492297:TRPM8 protein, mouse; D050051:Transient Receptor Potential Channels; C475685:Trpa1 protein, mouse; C480976:Trpa1 protein, rat; C498947:Trpm8 protein, rat