Endothelin‐1 Potentiates Capsaicin‐induced Constriction of Human Adipose Arterioles

Field: Medicine (Health Sciences)

Mechanosensitive Ca 2+ ‐permeable channels of the transient receptor potential vanilloid (TRPV) family, have emerged as important regulators of vascular tone. TRPV1, the first identified member of the TRPV subfamily, has been extensively studied in rodent and other animal vascular beds. On perivascular sensory nerves and endothelial cells (EC), TRPV1 activation is shown to cause vasodilation; whereas activation of smooth muscle (VSMC) TRPV1 causes vasoconstriction. Their role, however, in the human vasculature remains poorly understood. We hypothesized that TRPV1 channels are expressed in the human vasculature and influence vascular tone upon activation. The objective of the current study was to characterize the expression and vasomotor function of TRPV1 channels in human coronary and adipose arterioles (HCAs & HAAs respectively). RT‐PCR analysis revealed the presence of TRPV1 transcripts in HCAs and HAAs isolated from multiple subjects. Consistent with mRNA expression, TRPV1 was detected in membrane fractions of HCAs and HAAs using immunoblotting. Upon examination of the vasomotor effect of capsaicin (TRPV1‐selective agonist) on HAAs, we found that bath application of capsaicin (10 −9 – 10 −6 M) induced dose‐dependent constriction of both endothelium‐intact (31.6 ± 9% at 10 −6 M; n=6) and denuded HAAs (42.6 ± 10.6% at 10 −6 M; n=5), suggesting a vasoconstrictive role for VSMC TRPV1 channels in the human microcirculation. This response was inhibited by the TRPV1‐selective inhibitor, SB366791 (0.2 ± 0.1% at 10 −6 M; n=6 intact vessels), thus demonstrating the specificity of capsaicin for TRPV1. To investigate the mechanism of capsaicin‐induced constriction, we examined changes in global intracellular calcium concentration ([Ca 2+ ] i ) in native human VSMC. Capsaicin (10 −7 –10 −6 M) induced dose‐dependent increases in [Ca 2+ ] i in native VSMC, which were inhibited by SB366791 (1 μM), again supporting a vasoconstrictive role for VSMC TRPV1. To further explore the physiological significance of TRPV1 channels in vasomotor control, we investigated if TRPV1 channel function is modulated by the physiological vasoconstrictor, endothelin‐1 (ET‐1). HAAs were preconstricted with ET‐1 to 10–15% of their baseline diameter before bath application of increasing doses of capsaicin (10 −9 – 10 −6 M). Capsaicin‐induced constriction was potentiated by ET‐1 in both endothelium‐intact (50.1 ± 6.7% at 10 −6 M; n=9) and denuded (52 ± 5.2% at 10 −6 M; n=5) arterioles. These results indicate that TRPV1 channels are expressed and functional in the human microvasculature and that their activity is modulated by endogenous vasoconstrictors such as ET‐1. Future studies are required to elucidate the mechanism of ET‐1 induced potentiation of TRPV1‐mediated constriction. Support or Funding Information Support for this research was provided by the National Heart, Lung and Blood Institute Grant RO1‐HL 096647 and American Heart Association Grant 18PRE34060242/Ankush Korishettar/2018. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .