What are transient receptor potential cation channels, subfamily 1, and what role do they play in pain transmission?
The transient receptor potential cation channels, subfamily 1 (TRPV1) channel is a capsaicin and vanilloid receptor 1 that is expressed on pain fibers. TRPV1 provides a sensation of scalding heat and pain when activated. It also functions in the detection and regulation of body temperature. The channel is activated by capsaicin, causing an influx of intracellular calcium. High levels of intracellular calcium will overwhelm the mitochondria, resulting in axonal death. A high-dose capsaicin patch (8%) is currently marketed for the treatment of postherpetic neuralgia. A single 60-minute application can result in 3 months of pain relief, due to the axonal death of TRPV1-expressing peripheral nerve fibers. Clinical effectiveness has been mixed, but a recent study suggested that patients with cold and pinprick hyperalgesia had a positive predictive value for response to high-dose capsaicin patch application. There has been interest in the systemic delivery of TRPV1 channel antagonists; however, systemic delivery results in hyperthermia and increased thermal sensation thresholds. A phase II study was stopped early due to futility.