TRPV channels in human skeletal muscle feed arteries: implications for vascular function.

What is the central question of this study? We sought to determine whether human skeletal muscle feed arteries (SFMAs) express TRPV channels and what role they play in modulating vascular function. What is the main finding and its importance? Human SMFAs do express functional TRPV channels that modulate vascular function, specifically opposing α-adrenergic receptor-mediated vasocontraction and potentiating vasorelaxation, in an endothelium-dependent manner, as evidenced by the α -receptor-mediated responses. Thus, the vasodilatory role of TRPV channels, and their ligand capsaicin, could be a potential therapeutic target for improving vascular function. Additionally, given the 'sympatholytic' effect of TRPV activation and known endogenous activators (anandamide, reactive oxygen species, H , etc.), TRPV channels might contribute to functional sympatholysis during exercise. To examine the role of the transient receptor potential vanilloid type 1 (TRPV ) ion channel in the vascular function of human skeletal muscle feed arteries (SMFAs) and whether activation of this heat-sensitive receptor could be involved in modulating vascular function, SMFAs from 16 humans (63 ± 5 years old, range 41-89 years) were studied using wire myography with capsaicin (TRPV agonist) and without (control). Specifically, phenylephrine (α -adrenergic receptor agonist), dexmedetomidine (α -adrenergic receptor agonist), ACh and sodium nitroprusside concentration-response curves were established to assess the role of TRPV channels in α-receptor-mediated vasocontraction as well as endothelium-dependent and -independent vasorelaxation, respectively. Compared with control conditions, capsaicin significantly attenuated maximal vasocontraction in response to phenylephrine [control, 52 ± 8% length-tension (LT ) and capsaicin, 21 ± 5%LT ] and dexmedetomidine (control, 29 ± 12%LT and capsaicin, 2 ± 3%LT ), while robustly enhancing maximal vasorelaxation with ACh (control, 78 ± 8% vasorelaxation and capsaicin, 108 ± 13% vasorelaxation) and less clearly enhancing the sodium nitroprusside response. Denudation of the endothelium greatly attenuated the maximal ACh-induced vasorelaxation equally in the control and capsaicin conditions (∼17% vasorelaxation) and abolished the attenuating effect of capsaicin on the maximal phenylephrine response (denuded + capsaicin, 61 ± 20%LT ). Immunohistochemistry identified a relatively high density of TRPV channels in the endothelium compared with the smooth muscle of the SMFAs, but because of the far greater volume of smooth muscle, total TRPV protein content was not significantly attenuated by denudation. Thus, SMFAs ubiquitously express functional TRPV channels, which alter vascular function, in terms of α -receptors, in a predominantly endothelium-dependent manner, conceivably contributing to the functional sympatholysis and unveiling a therapeutic target.