Cutaneous thermoreceptors and nociceptors (ThermoTRP channels)

Cutaneous thermoreceptors and nociceptors are specialized sensory receptors located in the skin that detect temperature changes and thermal pain. These receptors consist of free nerve endings of sensory neurons terminating in the epidermis and dermis. The molecular basis of thermosensation involves the transient receptor potential (TRP) ion channel family, which act as thermoreceptors and function as thermostat molecules with specific threshold temperatures for activation. The thermoreceptor family includes multiple ion channels with distinct temperature sensitivities. For cold sensation, TRPM8 mediates responses to innocuous cold temperatures (below 26°C) and is also activated by cooling compounds like menthol. TRPA1 responds to noxious cold (around 17.5°C) and plays a significant role in pathological cold signaling, particularly in cold hypersensitivity associated with nerve injury and chemotherapy. For warm and heat sensation, several channels are involved. TRPV3 and TRPV4 detect innocuous warm temperatures (over 27°C and under 42°C) and are highly expressed in skin epidermal keratinocytes. TRPV1 serves as the primary noxious heat sensor with a threshold of 42°C and is also activated by capsaicin from chili peppers, producing burning sensations. Additional noxious heat sensors include TRPV2 (threshold 52°C), TRPM3 (threshold 40°C), and ANO1 (threshold 44°C). These thermoreceptors are non-selective cation channels with structures similar to voltage-dependent potassium channels, containing six transmembrane segments that form tetramers. The sensory information is transmitted through either thinly myelinated Aδ fibers (for cold and sharp pain) or unmyelinated C fibers (for warmth, noxious heat, and dull pain), with cell bodies located in dorsal root ganglia and synaptic terminals in the spinal cord dorsal horn. ThermoTRP channels function as physiological thermostats, exhibiting threshold responses where they activate only when temperature falls below or rises above their set-point temperatures. They are also multimodal receptors that respond to chemical compounds, allowing for pharmacological modulation. The heat sensitivity of these channels can be regulated by various factors including protein kinase C isoforms (PKCβII and PKCε), membrane lipid PIP2, and scaffolding proteins like AKAP79/150. Sensory neurons employ multiple and redundant heat sensors, likely to ensure robust detection of potentially damaging thermal stimuli. The varied expression and co-expression patterns of different TRP channels across neuronal populations create a gradient of temperature sensing capabilities, enabling precise discrimination of different thermal ranges from innocuous cooling to noxious heat.

Other names

ThermoreceptorsTemperature sensorsThermal receptorsTRP channels (transient receptor potential channels)ThermoTRP channelsCutaneous temperature receptorsSkin thermoreceptorsThermal nociceptors

Ion channel activation by thermal stimuli. Temperature-dependent gating. Chemical agonist activation. Depolarization of sensory neurons. Action potential generation. Calcium and sodium ion influx. Receptor potential generation.