Inorganic Polyphosphate Modulates TRPM8 Channels

Polyphosphate (polyP) is an inorganic polymer built of tens to hundreds of phosphates, linked by high-energy phosphoanhydride bonds. PolyP forms complexes and modulates activities of many proteins including ion channels. Here we investigated the role of polyP in the function of the transient receptor potential melastatin 8 (TRPM8) channel. Using whole-cell patch-clamp and fluorescent calcium measurements we demonstrate that enzymatic breakdown of polyP by exopolyphosphatase (scPPX1) inhibits channel activity in human embryonic kidney and F-11 neuronal cells expressing TRPM8. We demonstrate that the TRPM8 channel protein is associated with polyP. Furthermore, addition of scPPX1 altered the voltage-dependence and blocked the activity of the purified TRPM8 channels reconstituted into planar lipid bilayers, where the activity of the channel was initiated by cold and menthol in the presence of phosphatidylinositol 4,5-biphosphate (PtdIns(4,5)P2). The biochemical analysis of the TRPM8 protein also uncovered the presence of poly-(R)-3-hydroxybutyrate (PHB), which is frequently associated with polyP. We conclude that the TRPM8 protein forms a stable complex with polyP and its presence is essential for normal channel activity

Voltage-Dependent Gating in a “Voltage Sensor-Less” Ion Channel

An unusual mechanism of ion channel regulation generates voltage-dependent gating in the absence of a canonical voltage-sensing domain

Evolution of Thermal Response Properties in a Cold-Activated TRP Channel

Animals sense changes in ambient temperature irrespective of whether core body temperature is internally maintained (homeotherms) or subject to environmental variation (poikilotherms). Here we show that a cold-sensitive ion channel, TRPM8, displays dramatically different thermal activation ranges in frogs versus mammals or birds, consistent with variations in these species' cutaneous and core body temperatures. Thus, somatosensory receptors are not static through evolution, but show functional diversity reflecting the characteristics of an organism's ecological niche

TRPV1 enhances the afferent response to P2X receptor activation in the mouse urinary bladder

Both TRPV1 and P2X receptors present on bladder sensory nerve fibres have been implicated in mechanosensation during bladder filling. The aim of this study was to determine possible interactions between these receptors in modulating afferent nerve activity. In wildtype (TRPV1+/+) and TRPV1 knockout (TRPV1−/−) mice, bladder afferent nerve activity, intravesical pressure, and luminal ATP and acetylcholine levels were determined and also intracellular calcium responses of dissociated pelvic DRG neurones and primary mouse urothelial cells (PMUCs). Bladder afferent nerve responses to the purinergic agonist αβMethylene-ATP were depressed in TRPV1−/− mice (p ≤ 0.001) and also in TRPV1+/+ mice treated with the TRPV1-antagonist capsazepine (10 µM; p ≤ 0.001). These effects were independent of changes in bladder compliance or contractility. Responses of DRG neuron to αβMethylene-ATP (30 µM) were unchanged in the TRPV1−/− mice, but the proportion of responsive neurones was reduced (p ≤ 0.01). Although the TRPV1 agonist capsaicin (1 µM) did not evoke intracellular responses in PMUCs from TRPV1+/+ mice, luminal ATP levels were reduced in the TRPV1−/− mice (p ≤ 0.001) compared to wildtype. TRPV1 modulates P2X mediated afferent responses and provides a mechanistic basis for the decrease in sensory symptoms observed following resiniferatoxin and capsaicin treatment for lower urinary tract symptoms

Citral Sensing by TRANSient Receptor Potential Channels in Dorsal Root Ganglion Neurons

Transient receptor potential (TRP) ion channels mediate key aspects of taste, smell, pain, temperature sensation, and pheromone detection. To deepen our understanding of TRP channel physiology, we require more diverse pharmacological tools. Citral, a bioactive component of lemongrass, is commonly used as a taste enhancer, as an odorant in perfumes, and as an insect repellent. Here we report that citral activates TRP channels found in sensory neurons (TRPV1 and TRPV3, TRPM8, and TRPA1), and produces long-lasting inhibition of TRPV1–3 and TRPM8, while transiently blocking TRPV4 and TRPA1. Sustained citral inhibition is independent of internal calcium concentration, but is state-dependent, developing only after TRP channel opening. Citral's actions as a partial agonist are not due to cysteine modification of the channels nor are they a consequence of citral's stereoisoforms. The isolated aldehyde and alcohol cis and trans enantiomers (neral, nerol, geranial, and geraniol) each reproduce citral's actions. In juvenile rat dorsal root ganglion neurons, prolonged citral inhibition of native TRPV1 channels enabled the separation of TRPV2 and TRPV3 currents. We find that TRPV2 and TRPV3 channels are present in a high proportion of these neurons (94% respond to 2-aminoethyldiphenyl borate), consistent with our immunolabeling experiments and previous in situ hybridization studies. The TRPV1 activation requires residues in transmembrane segments two through four of the voltage-sensor domain, a region previously implicated in capsaicin activation of TRPV1 and analogous menthol activation of TRPM8. Citral's broad spectrum and prolonged sensory inhibition may prove more useful than capsaicin for allodynia, itch, or other types of pain involving superficial sensory nerves and skin