Abstract
Cold sensation is an important and fundamental sense for animals and it is known to be affected by ambient temperature. Transient Receptor Potential Melastatin 8 (TRPM8), a nonselective cation channel expressed in a subset of peripheral afferent fibers, acts as a cold sensor, having an activation threshold of ∼28°C. Although the cold temperature threshold of TRPM8 is affected by menthol or pH, ambient temperature has not been reported to affect it. Because the cold temperature threshold was thought to be unchanged by alterations in ambient temperature, the relativity of temperature sensing in different ambient temperatures could not be understood at the level of molecular function of thermosensitive TRP channels. Here, we show that ambient temperature changed the temperature threshold for activation of human and rat TRPM8 in a heterologous expression system and cold responses in mouse DRG neurons. Moreover, reducing the level of cellular phosphatidylinositol 4,5-bisphosphate (PIP2) attenuated changes in the cold temperature threshold after alterations in ambient temperature. A single amino acid mutation at position 1008 in the C terminus of TRPM8 (arginine to glutamine) also attenuated changes in the cold temperature threshold induced by ambient temperature. These findings suggest that ambient temperature does affect the temperature threshold for TRPM8 activation through interaction of PIP2.