Arteries are finely tuned thermosensors regulating myogenic tone and blood flow.

In response to changing blood pressure, arteries adjust their caliber to control perfusion. This vital autoregulatory property, termed vascular myogenic tone, stabilizes downstream capillary pressure. We discovered that tissue temperature critically determines myogenic tone. Heating steeply activates tone in skeletal muscle, gut, brain and skin arteries with temperature coefficients ( Q 10 ) of ∼11-20. Further, arterial thermosensitivity is tuned to resting tissue temperatures, making myogenic tone sensitive to small thermal fluctuations. Interestingly, temperature and intraluminal pressure are sensed largely independently and integrated to trigger myogenic tone. We show that TRPV1 and TRPM4 mediate heat-induced tone in skeletal muscle arteries. Variations in tissue temperature are known to alter vascular conductance; remarkably, thermosensitive tone counterbalances this effect, thus protecting capillary integrity and fluid balance. In conclusion, thermosensitive myogenic tone is a fundamental homeostatic mechanism regulating tissue perfusion. One-Sentence Summary: Arterial blood pressure and temperature are integrated via thermosensitve ion channels to produce myogenic tone.

TRPV1 in arteries enables a rapid myogenic tone.

Arterioles maintain blow flow by adjusting their diameter in response to changes in local blood pressure. In this process called the myogenic response, a vascular smooth muscle mechanosensor controls tone predominantly through altering the membrane potential. In general, myogenic responses occur slowly (minutes). In the heart and skeletal muscle, however, tone is activated rapidly (tens of seconds) and terminated by brief (100 ms) arterial constrictions. Previously, we identified extensive expression of TRPV1 in the smooth muscle of arterioles supplying skeletal muscle, heart and fat. Here we reveal a critical role for TRPV1 in the rapid myogenic tone of these tissues. TRPV1 antagonists dilated skeletal muscle arterioles in vitro and in vivo, increased coronary flow in isolated hearts, and transiently decreased blood pressure. All of these pharmacologic effects were abolished by genetic disruption of TRPV1. Stretch of isolated vascular smooth muscle cells or raised intravascular pressure in arteries triggered Ca2+ signalling and vasoconstriction. The majority of these stretch-responses were TRPV1-mediated, with the remaining tone being inhibited by the TRPM4 antagonist, 9-phenantrol. Notably, tone developed more quickly in arteries from wild-type compared with TRPV1-null mice. Furthermore, the immediate vasodilation following brief constriction of arterioles depended on TRPV1, consistent with a rapid deactivation of TRPV1. Pharmacologic experiments revealed that membrane stretch activates phospholipase C/protein kinase C signalling combined with heat to activate TRPV1, and in turn, L-type Ca2+ channels. These results suggest a critical role, for TRPV1 in the dynamic regulation of myogenic tone and blood flow in the heart and skeletal muscle. KEY POINTS: We explored the physiological role of TRPV1 in vascular smooth muscle. TRPV1 antagonists dilated skeletal muscle arterioles both ex vivo and in vivo, increased coronary perfusion and decreased systemic blood pressure. Stretch of arteriolar myocytes and increases in intraluminal pressure in arteries triggered rapid Ca2+ signalling and vasoconstriction respectively. Pharmacologic and/or genetic disruption of TRPV1 significantly inhibited the magnitude and rate of these responses. Furthermore, disrupting TRPV1 blunted the rapid vasodilation evoked by arterial constriction. Pharmacological experiments identified key roles for phospholipase C and protein kinase C, combined with temperature, in TRPV1-dependent arterial tone. These results show that TRPV1 in arteriolar myocytes dynamically regulates myogenic tone and blood flow in the heart and skeletal muscle.

TRPV1 expressed throughout the arterial circulation regulates vasoconstriction and blood pressure.

KEY POINTS: The functional roles of the capsaicin receptor, TRPV1, outside of sensory nerves are unclear. We mapped TRPV1 in the mouse circulation, revealing extensive expression in the smooth muscle of resistance arterioles supplying skeletal muscle, heart and adipose tissue.  Activation of TRPV1 in vascular myocytes constricted arteries, reduced coronary flow in isolated hearts and increased systemic blood pressure. These functional effects were retained after sensory nerve ablation, indicating specific signalling by arterial TRPV1.  TRPV1 mediated the vasoconstrictive and blood pressure responses to the endogenous inflammatory lipid lysophosphatidic acid.  These results show that TRPV1 in arteriolar myocytes modulates regional blood flow and systemic blood pressure, and suggest that TRPV1 may be a target of vasoactive inflammatory mediators. ABSTRACT: The capsaicin receptor, TRPV1, is a key ion channel involved in inflammatory pain signalling. Although mainly studied in sensory nerves, there are reports of TRPV1 expression in isolated segments of the vasculature, but whether the channel localizes to vascular endothelium or smooth muscle is controversial and the distribution and functional roles of TRPV1 in arteries remain unknown. We mapped functional TRPV1 expression throughout the mouse arterial circulation. Analysis of reporter mouse lines TRPV1PLAP-nlacZ and TRPV1-Cre:tdTomato combined with Ca2+ imaging revealed specific localization of TRPV1 to smooth muscle of terminal arterioles in the heart, adipose tissue and skeletal muscle. Capsaicin evoked inward currents (current density ∼10% of sensory neurons) and raised intracellular Ca2+ levels in arterial smooth muscle cells, constricted arterioles ex vivo and in vivo and increased systemic blood pressure in mice and rats. Further, capsaicin markedly and dose-dependently reduced coronary flow. Pharmacological and/or genetic disruption of TRPV1 abolished all these effects of capsaicin as well as vasoconstriction triggered by lysophosphatidic acid, a bioactive lipid generated by platelets and atherogenic plaques. Notably, ablation of sensory nerves did not affect the responses to capsaicin revealing a vascular smooth muscle-restricted signalling mechanism. Moreover, unlike in sensory nerves, TRPV1 function in arteries was resistant to activity-induced desensitization. Thus, TRPV1 activation in vascular myocytes enables a persistent depolarizing current, leading to constriction of coronary, skeletal muscle and adipose arterioles and a sustained increase in systemic blood pressure.

Inhibition of Ligand-Gated TRPA1 by General Anesthetics.

Several general anesthetics (GAs) produce pain or irritation upon administration, and this occurs predominantly through the activation of the nociceptive ion channel, transient receptor potential ankyrin type 1 (TRPA1). However, the effects of GAs on agonist-mediated TRPA1 activity are unclear. Here we show that a diverse range of noxious and non-noxious volatile anesthetics, at clinically relevant concentrations, inhibit ligand-activated TRPA1 currents. These effects are species-specific; GAs blocks rodent TRPA1 without affecting the Drosophila ortholog. Furthermore, propofol inhibits rodent but not human TRPA1. Analysis of chimeric TRPA1 proteins and mutagenesis combined reveals two amino acid residues located in the S5 domain, Ser876 and Thr877, that are critical for the inhibitory effects of isoflurane and propofol. Introduction of these residues into Drosophila TRPA1 confers anesthetic inhibition. Furthermore, several residues lining the presumptive binding pocket for noxious GAs are not required for the inhibitory effects of GAs. We conclude that anesthetics inhibit TRPA1 by interacting at a site distinct from the activation site. The inhibitory effects of GAs at TRPA1 may contribute to the diverse pharmacological action of these drugs. SIGNIFICANCE STATEMENT: We show that both noxious and non-noxious general anesthetics inhibit agonist-evoked transient receptor potential ankyrin type 1 (TRPA1) activity and identify critical amino acid residues located in the pore domain. Inhibition of TRPA1 may affect pain and vascular signaling during anesthesia.

Identification of a putative binding site critical for general anesthetic activation of TRPA1.

General anesthetics suppress CNS activity by modulating the function of membrane ion channels, in particular, by enhancing activity of GABAA receptors. In contrast, several volatile (isoflurane, desflurane) and i.v. (propofol) general anesthetics excite peripheral sensory nerves to cause pain and irritation upon administration. These noxious anesthetics activate transient receptor potential ankyrin repeat 1 (TRPA1), a major nociceptive ion channel, but the underlying mechanisms and site of action are unknown. Here we exploit the observation that pungent anesthetics activate mammalian but not Drosophila TRPA1. Analysis of chimeric Drosophila and mouse TRPA1 channels reveal a critical role for the fifth transmembrane domain (S5) in sensing anesthetics. Interestingly, we show that anesthetics share with the antagonist A-967079 a potential binding pocket lined by residues in the S5, S6, and the first pore helix; isoflurane competitively disrupts A-967079 antagonism, and introducing these mammalian TRPA1 residues into dTRPA1 recapitulates anesthetic agonism. Furthermore, molecular modeling predicts that isoflurane and propofol bind to this pocket by forming H-bond and halogen-bond interactions with Ser-876, Met-915, and Met-956. Mutagenizing Met-915 or Met-956 selectively abolishes activation by isoflurane and propofol without affecting actions of A-967079 or the agonist, menthol. Thus, our combined experimental and computational results reveal the potential binding mode of noxious general anesthetics at TRPA1. These data may provide a structural basis for designing drugs to counter the noxious and vasorelaxant properties of general anesthetics and may prove useful in understanding effects of anesthetics on related ion channels.

Intrinsic Photosensitivity Enhances Motility of T Lymphocytes.

Sunlight has important biological effects in human skin. Ultraviolet (UV) light striking the epidermis catalyzes the synthesis of Vitamin D and triggers melanin production. Although a causative element in skin cancers, sunlight is also associated with positive health outcomes including reduced incidences of autoimmune diseases and cancers. The mechanisms, however, by which light affects immune function remain unclear. Here we describe direct photon sensing in human and mouse T lymphocytes, a cell-type highly abundant in skin. Blue light irradiation at low doses (<300 mJ cm-2) triggers synthesis of hydrogen peroxide (H2O2) in T cells revealed by the genetically encoded reporter HyPerRed. In turn, H2O2 activates a Src kinase/phospholipase C-γ1 (PLC-γ1) signaling pathway and Ca2+ mobilization. Pharmacologic inhibition or genetic disruption of Lck kinase, PLC-γ1 or the T cell receptor complex inhibits light-evoked Ca2+ transients. Notably, both light and H2O2 enhance T-cell motility in a Lck-dependent manner. Thus, T lymphocytes possess intrinsic photosensitivity and this property may enhance their motility in skin.

Sex-dependent expression of TRPV1 in bladder arterioles.

Transient receptor potential vanilloid type 1 (TRPV1) is a major nociceptive ion channel implicated in bladder physiology and/or pathophysiology. However, the precise expression of TRPV1 in neuronal vs. nonneuronal bladder cells is uncertain. Here we used reporter mouse lines (TRPV1-Cre:tdTomato and TRPV1PLAP-nlacZ) to map expression of TRPV1 in postnatal bladder. TRPV1 was not detected in the urothelium, however, we found marked expression of TRPV1 lineage in sensory nerves, and surprisingly, in arterial/arteriolar smooth muscle (ASM) cells. Tomato fluorescence was prominent in the vesical arteries and in small-diameter (15-40 µm) arterioles located in the suburothelial layer with a near equal distribution in bladder dome and base. Notably, arteriolar TRPV1 expression was greater in females than in males and increased in both sexes after 90 days of age, suggesting sex hormone and age dependency. Analysis of whole bladder and vesical artery TRPV1 mRNA revealed a similar sex and developmental dependence. Pharmacological experiments confirmed functional TRPV1 protein expression; capsaicin increased intracellular Ca2+ in ∼15% of ASM cells from wild-type female bladders, but we observed no responses to capsaicin in bladder arterioles isolated from TRPV1-null mice. Furthermore, capsaicin triggered arteriole constriction that was rapidly reversed by the TRPV1 antagonist, BCTC. These data show that predominantly in postpubertal female mice, bladder ASM cells express functional TRPV1 channels that may act to constrict arterioles. TRPV1 may therefore play an important role in regulating the microcirculation of the female bladder, and this effect may be of significance during inflammatory conditions.