The TRPM3 ion channel mediates nociception but not itch evoked by endogenous pruritogenic mediators

During the molecular transduction of itch, the stimulation of pruriceptors on sensory fibers leads to the activation or sensitization of ion channels, which results in a consequent depolarization of the neurons. These ion channels mostly belong to the transient receptor potential (TRP) channels, which are involved in nociception and thermosensation. In particular, TRPV1 and TRPA1 were described in the transduction of both thermal nociception as well as histaminergic and non-histaminergic itch. The thermosensitive TRPM3 plays an indispensable role in heat nociception together with TRPV1 and TRPA1. However, the role of TRPM3 in the development of pruritus has not been studied yet. Therefore, in this study we aimed at investigating the potential role of TRPM3 in the transduction of pruritus and pain by investigating itch- and nociception-related behavior of Trpm3+/+ and Trpm3-/- mice, and by studying the activation of somatosensory neurons isolated from trigeminal ganglia upon application of algogenic and pruritogenic substances. Activators of TRPM3 evoked only nocifensive responses, but not itch in Trpm3+/+ animals, and these nocifensive responses were abolished in the Trpm3-/- strain. Histamine and endogenous non-histaminergic pruritogens induced itch in both Trpm3+/+ and Trpm3-/- mice to a similar extent. Genetic deletion or pharmacological blockade diminished TRPM3 mediated Ca2+ responses of sensory neurons, but did not affect responses evoked by pruritogenic substances. Our results demonstrate that, in contrast to other thermosensitive TRP channels, TRPM3 selectively mediates nociception, but not itch sensation, and suggest that TRPM3 is a promising candidate to selectively target pain sensation.

Volatile anaesthetics inhibit the thermosensitive nociceptor ion channel transient receptor potential melastatin 3 (TRPM3)

BACKGROUND

Volatile anaesthetics (VAs) are the most widely used compounds to induce reversible loss of consciousness and maintain general anaesthesia during surgical interventions. Although the mechanism of their action is not yet fully understood, it is generally believed, that VAs depress central nervous system functions mainly through modulation of ion channels in the neuronal membrane, including 2-pore-domain K+ channels, GABA and NMDA receptors. Recent research also reported their action on nociceptive and thermosensitive TRP channels expressed in the peripheral nervous system, including TRPV1, TRPA1, and TRPM8. Here, we investigated the effect of VAs on TRPM3, a less characterized member of the thermosensitive TRP channels playing a central role in noxious heat sensation.

METHODS

We investigated the effect of VAs on the activity of recombinant and native TRPM3, by monitoring changes in the intracellular Ca²⁺ concentration and measuring TRPM3-mediated transmembrane currents.

RESULTS

All the investigated VAs (chloroform, halothane, isoflurane, sevoflurane) inhibited both the agonist-induced (pregnenolone sulfate, CIM0216) and heat-activated Ca²⁺ signals and transmembrane currents in a concentration dependent way in HEK293T cells overexpressing recombinant TRPM3. Among the tested VAs, halothane was the most potent blocker (IC₅₀ = 0.52 ± 0.05 mM). We also investigated the effect of VAs on native TRPM3 channels expressed in sensory neurons of the dorsal root ganglia. While VAs activated certain sensory neurons independently of TRPM3, they strongly and reversibly inhibited the agonist-induced TRPM3 activity.

CONCLUSIONS

These data provide a better insight into the molecular mechanism beyond the analgesic effect of VAs and propose novel strategies to attenuate TRPM3 dependent nociception.

TRPA1 Acts in a Protective Manner in Imiquimod-Induced Psoriasiform Dermatitis in Mice

This study revealed the modulatory role of transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1) cation channels in the Aldara-induced (5% imiquimod) murine psoriasis model using selective antagonists and genetically altered animals. We have also developed a refined localized model to enable internal controls and reduce systemic effects. Skin pathology was quantified by measuring skin thickness, scaling, blood flow, and analyzing dermal cellular infiltrate, whereas nocifensive behaviors were also observed. Cytokine gene expression profiles were measured ex vivo. Psoriasiform dermatitis was significantly enhanced in TRPA1 knockout mice and with TRPA1 antagonist (A967079) treatment. By comparison, symptoms were decreased when TRPV1 function was inhibited. Imiquimod induced Ca²⁺ influx in TRPA1-, but not in TRPV1-expressing cell lines. Immunohistochemical studies revealed that CD4+ T helper cells express TRPA1 but not TRPV1 ion channels in mice skin. Compared with the TRPV1 knockout animals, additional elimination of the TRPA1 channels in the TRPV1/TRPA1 double knockout mice did not modify the outcome of the imiquimod-induced reaction, further supporting the dominant role of TRPV1 in the process. Our results suggest that the protective effects in psoriasiform dermatitis can be mediated by the activation of neuronal and nonneuronal TRPA1 receptors.

Human podocytes express functional thermosensitive TRPV channels

BACKGROUND AND PURPOSE

Heat-sensitive transient receptor potential vanilloid (TRPV) channels are expressed in various epithelial tissues regulating, among else, barrier functions. Their expression is well established in the distal nephron; however, we have no data about their presence in podocytes. As podocytes are indispensable in the formation of the glomerular filtration barrier, we investigated the presence and function of Ca²⁺ -permeable TRPV1-4 channels in human podocyte cultures.

EXPERIMENTAL APPROACH

Expression of TRPV1-4 channels was investigated at protein (immunocytochemistry, Western blot) and mRNA (Q-PCR) level in a conditionally immortalized human podocyte cell line. Channel function was assessed by measuring intracellular Ca²⁺ concentration using Flou-4 Ca²⁺ -indicator dye and patch clamp electrophysiology upon applying various activators and inhibitors.

KEY RESULTS

Thermosensitive TRP channels were expressed in podocytes. The TRPV1-specific agonists capsaicin and resiniferatoxin did not affect the intracellular Ca²⁺ concentration. Cannabidiol, an activator of TRPV2 and TRPV4 channels, induced moderate Ca²⁺ -influxes, inhibited by both tranilast and HC067047, blockers of TRPV2 and TRPV4 channels respectively. The TRPV4-specific agonists GSK1016790A and 4α-phorbol 12,13-didecanoate induced robust Ca²⁺ -signals which were abolished by HC067047. Non-specific agonists of TRPV3 channels induced marked Ca²⁺ transients. However, TRPV3 channel blockers, ruthenium red and isopentenyl diphosphate only partly inhibited the responses and TRPV3 silencing was ineffective suggesting remarkable off-target effects of the compounds.

CONCLUSION AND IMPLICATIONS

Our results indicate the functional presence of TRPV4 and other thermosensitive TRPV channels in human podocytes and raise the possibility of their involvement in the regulation of glomerular filtration barrier.

Effect of type of early infant feeding on fatty acid composition of plasma lipid classes in full-term infants during the second 6 months of life

BACKGROUND

Previously, the authors found significantly higher arachidonic and docosahexaenoic acid values in plasma lipids in 2-month-old full-term infants fed human milk than in those receiving formula. This is the report of data obtained in full-term infants during the second half of the first year of life.

METHODS

Healthy, full-term infants fed human milk (n = 12) or formula without preformed long-chain polyunsaturated fatty acids (n = 12) were investigated. Fatty acid composition of plasma lipid classes was determined by high-resolution capillary gas-liquid chromatography.

RESULTS

Linoleic acid acid values in plasma phospholipids (18.5 [3.94] vs. 20.79 [4.34]) and gamma-linolenic acid values in plasma cholesteryl esters (0.17 [0.09] vs. 0.27 [0.20]) and triacylglycerols (0.27 [0.18] vs. 0.46 [0.27]) were significantly (P < 0.05) lower in breast-fed infants than in those receiving formula. Data are percentage weight by weight shown as median (range from 1st to 3rd quartile) for breast-fed vs. formula fed infants, respectively. In contrast, arachidonic acid values in plasma phospholipids (10.05 [2.90] vs. 7.03 [1.87]; P < 0.01), cholesteryl esters (7.54 [3.58] vs. 4.09 [1.81]; P < 0.05), and triacylglycerols (1.28 [0.84] vs. 0.80 [0.39]; P < 0.05), as well as docosahexaenoic acid values in plasma phospholipids (1.92 [0.36] vs. 1.02 [0.31]; P < 0.001), cholesteryl esters (0.39 [0.13] vs. 0.15 [0.13]; P < 0.001), and triacylglycerols (0.17 [0.17] vs. 0.09 [0.04]; P < 0.01) were significantly higher in infants fed human milk than in those receiving formula.

CONCLUSION

Healthy, full-term infants fed formula without preformed dietary long-chain polyunsaturated fatty acids are unable to match the arachidonic and docosahexaenoic acid status of breast-fed infants even during the second half of the first year of life.