The transient receptor potential type V1 channel (vanilloid receptor 1, TRPV1) is a Ca 2ϩ -permeable nonspecific cation channel activated by various painful stimuli including ischemia. We hypothesized that TRPV1 is expressed in the arterioles and is involved in the regulation of microvascular tone. We found that TRPV1 stimulation by capsaicin (intra-arterial administration) of the isolated, perfused right hind limb of the rat increased vascular resistance (by 98 Ϯ 21 mm Hg at 10 g) in association with decreased skeletal muscle perfusion and elevation of skin perfusion (detected by dual-channel laser Doppler flowmetry). Denervation of the hind limb did not affect capsaicin-evoked changes in vascular resistance and tissue perfusion in the hind limb but reduced the elevation of perfusion in the skin. In isolated, pressurized skeletal (musculus gracilis) muscle arterioles (diameter, 147 Ϯ 35 m), capsaicin had biphasic effects: at lower concentrations, capsaicin (up to 10 nM) evoked dilations (maximum, 32 Ϯ 13%), whereas higher concentrations (0.1-1 M) elicited substantial constrictions (maximum, 66 Ϯ 7%). Endothelium removal or inhibition of nitric-oxide synthase abolished capsaicin-induced dilations but did not affect arteriolar constriction. Expression of TRPV1 was detected by reverse transcriptase-polymerase chain reaction in the aorta and in cultured rat aortic vascular smooth muscle cells (A7r5). Immunohistochemistry revealed expression primarily in the smooth muscle layers of the gracilis arteriole. These data demonstrate the functional expression of TRPV1 in vascular smooth muscle cells mediating vasoconstriction of the resistance arteries. Because of the dual effects of TRPV1 stimulation on the arteriolar diameter (dilation in skin, constriction in skeletal muscle), we propose that TRPV1 ligands represent drug candidates for tissue-specific modulation of blood distribution.The transient receptor potential type V1 channel (vanilloid receptor-1, TRPV1) is a nonselective cation channel, structurally belonging to the transient receptor potential family of ion channels. TRPV1 is found in sensory C and A-␦ fibers (Caterina et al., 1997) and functions as a ligand-, proton-, and heat-activated molecular integrator of nociceptive stimuli in the periphery (Szallasi and Blumberg, 1999;

Transient receptor potential (TRP) cation channels are emerging in vascular biology. In particular, the expression of the capsaicin receptor (TRPV1) was reported in vascular smooth muscle cells. This study characterized the arteriolar TRPV1 function and expression in the rat. TRPV1 mRNA was expressed in various vascular beds. Six commercially available antibodies were tested for TRPV1 specificity. Two of them were specific (immunostaining was abolished by blocking peptides) for neuronal TRPV1 and one recognized vascular TRPV1. TRPV1 was expressed in blood vessels in the skeletal muscle, mesenteric and skin tissues, as well as in the aorta and carotid arteries. TRPV1 expression was found to be regulated at the level of individual blood vessels, where some vessels expressed, while others did not express TRPV1 in the same tissue sections. Capsaicin (a TRPV1 agonist) evoked constrictions in skeletal muscle arteries and in the carotid artery, but had no effect on the femoral and mesenteric arteries or the aorta. In blood vessels, TRPV1 expression was detected in most of the large arteries, but there were striking differences at level of the small arteries. TRPV1 activity was suppressed in some isolated arteries. This tightly regulated expression and function suggests a physiological role for vascular TRPV1.

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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.

BACKGROUND AND PURPOSE The transient receptor potential vanilloid 1 (TRPV1) plays a role in the activation of sensory neurons by various painful stimuli and is a therapeutic target. However, functional TRPV1 that affect microvascular diameter are also expressed in peripheral arteries and we attempted to characterize this receptor. EXPERIMENTAL APPROACH Sensory TRPV1 activation was measured in rats by use of an eye wiping assay. Arteriolar TRPV1‐mediated smooth muscle specific responses (arteriolar diameter, changes in intracellular Ca2+) were determined in isolated, pressurized skeletal muscle arterioles obtained from the rat and wild‐type or TRPV1−/− mice and in canine isolated smooth muscle cells. The vascular pharmacology of the TRPV1 agonists (potency, efficacy, kinetics of action and receptor desensitization) was determined in rat isolated skeletal muscle arteries. KEY RESULTS Capsaicin evoked a constrictor response in isolated arteries similar to that mediated by noradrenaline, this was absent in arteries from TRPV1 knockout mice and competitively inhibited by TRPV1 antagonist AMG9810. Capsaicin increased intracellular Ca2+ in the arteriolar wall and in isolated smooth muscle cells. The TRPV1 agonists evoked similar vascular constrictions (MSK‐195 and JYL‐79) or were without effect (resiniferatoxin and JYL‐273), although all increased the number of responses (sensory activation) in the eye wiping assay. Maximal doses of all agonists induced complete desensitization (tachyphylaxis) of arteriolar TRPV1 (with the exception of capsaicin). Responses to the partial agonist JYL‐1511 suggested 10% TRPV1 activation is sufficient to evoke vascular tachyphylaxis without sensory activation. CONCLUSIONS AND IMPLICATIONS Arteriolar TRPV1 have different pharmacological properties from those located on sensory neurons in the rat.