TRPV1

The transient receptor potential cation channel subfamily V (for vanilloid) subtype 1 (abbreviated TRPV1, from "transient receptor potential cation channel subfamily V member 1") is an ion channel in the sensory neurons of the vertebrate central and peripheral nervous systems. The coding gene is located on chromosome 17p13.2. As a "pain receptor", this ion channel is responsible for the perception of a series of tissue-damaging, often painful stimuli. Furthermore, the receptor plays a role in the sensation of tasty pungency.

TRPV1 is a transmembrane protein in the neurons of the central and peripheral nervous system. As a tetramer, it consists of four identical protein units with a closable channel in the middle. TRPV1 is activated by pain events. Thus by noxious heat (>42 or 43 °C), by a lowered pH value (<5.9), by itch-inducing substances. Activation results in the opening of the receptor-bound ion channel with influx of calcium ions. This leads to a depolarization of the cell membrane, to an action potential that propagates through the nerve pathways and ultimately leads to pain perception in the brain.

TRP channels are phylogenetically early signaling pathways (they can already be detected in yeast cells). The first TRP channel was identified in 1989 in connection with visual perception in Drosophila melanogaster. In a Drosophila mutant (trp343), it was shown that its photoreceptors responded to light stimuli only with a transient, i.e. rapidly inactivating, membrane current. In the non-mutated wild type, however, the current flow persisted as long as light hit the photoreceptor. The mutant protein -TRP- was cloned in 1989. Thus, the name "transient receptor potential" - TRP- refers to the description of a phenotype of a mutant of the fruit fly Drosophila melanogaster. TRP channels exert important functions in primary signaling pathways for the regulated influx of Ca2+ into a cell in both vertebrates and non-vertebrates. TRP channels in humans play an important role in the sensation of different types of taste (sweet, bitter, umami) as well as in the perception of pain, heat, warmth or cold, pressure and light. It is believed that some TRP channels in the body behave like microscopic thermosensors. So far, 28 TRP channel genes have been identified in mammals (Nilius B et al. 2011).

TRPV1 not only functions as a thermosensor, but also plays a role in various signal transduction pathways that are not necessarily related to nociception in response to tissue damage. Thus, in addition to being expressed in sensory fibers and distinct brain regions, TRPV1 is also expressed in neuronal fibers that innervate specific organs (bladder, prostate, lung, gastrointestinal tract, and dental neck). TRPV1 is also expressed in non-neuronal cells such as epidermal keratinocytes, bladder urothelial and smooth muscle cells, liver cells, granulocytes and macrophages.

TRPV1 agonists: Agonists of the receptor are capsaicin, psalmotoxins and vanillotoxins. Capsaicin activates the channel at a half-maximal effective concentration of EC50 ≈ 711 nM. Resiniferatoxin (RTX), a constituent of some spurge plants (Euphorbia resinifera), activates TRPV1 at EC50 ≈ 40 nM, making it an even more potent agonist than capsaicin. Both molecules carry a 3-methoxy-4-hydroxy-benzylamine group (vanillyl structure). Less potent are endogenous TRPV1 agonists such as arachidonic acid (AA) derivatives and lipoxygenase products of AA; they do not possess a vanillyl structure.

Furthermore, TRPV1 activity is influenced by a number of substances involved in inflammation, such as a mild increase in proton concentration, NGF, bradykinin, lipids, prostaglandins, PKA and PKC, and ATP. NGF and bradykinin potentiate TRPV1 activation by modulating intracellular PtdIn P2 ( phosphatidylinositol-4,5-bisphosphate).

TRPV1 antagonists: TRPV1 inhibited by capsazepine and iodo-resiniferatoxin and by the ion channel blocker ruthenium red.

The name "capsaicin receptor" has since been abandoned in favour of TRPV1 receptor.

The permanent irritation of the receptor by the pungent substance capsaicin leads to a kind of "desensitization" and consequently to a reduced sensitivity to the pain stimuli and itching mediated by TRPV1. At the same time, thermoreceptors in the skin are stimulated (increased sensation of warmth).

Capsaicin antagonists prevent the opening of the receptor pore through "receptor blockade" by interacting with the TRPV1 receptor. This prevents calcium ions from passing through the membrane and the development of a pain-inducing action potential. The temperature sensation is reduced (danger of burns).

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