Opposing vasomotor roles of TRPV1 and TRPV2 channels in the Human Adipose Microcirculation

Abstract

Mechanosensitive, Ca2+‐permeable channels of the transient receptor potential vanilloid (TRPV) family, especially TRPV4, have emerged as important regulators of vascular tone. Within the vasculature, TRPV channels are expressed in smooth muscle cells, endothelial cells and perivascular nerves. We have previously demonstrated that Ca2+ influx through endothelial TRPV4 channels mediates flow‐induced dilation (FID) of human coronary arterioles (HCAs) from subjects with coronary artery disease (CAD). Recent unpublished studies from our lab show that FID is not affected by TRPV4 inhibition in HCAs of subjects without CAD (non‐CAD), even though TRPV4 channels are similarly expressed in non‐CAD and CAD HCAs. Interestingly, FID of non‐CAD HCAs is inhibited by ruthenium red, a non‐selective TRPV channel blocker, suggesting the involvement of other TRPV channel subtypes. Moreover, endothelial TRPV1 channels have been previously shown to mediate FID in rodent arteries; whereas a functional role for endothelial TRPV2 channels has yet to be determined. Together, these data have led us to hypothesize that endothelial TRPV1/TRPV2 channels mediate FID of non‐CAD human coronary and adipose arterioles. The objective of the current study was to characterize the expression and vasomotor function of TRPV1 and TRPV2 channels in HCAs and human adipose arterioles (HAAs) from non‐CAD subjects. RT‐PCR analysis revealed the presence of TRPV1 and TRPV2 transcripts in HCAs and HAAs isolated from multiple subjects. Consistent with mRNA expression, both proteins were detected in membrane fractions of HCAs and HAAs using immunoblotting. We next examined the vasomotor effect of capsaicin, a TRPV1‐ selective agonist and cannabidiol, a TRPV2‐selective agonist, on freshly isolated HAAs. HAAs (100–250 μm) were cannulated under 60 mmHg and examined for diameter changes using videomicroscopy. Bath application of cannabidiol (10−7 – 10−5 M) induced dose‐dependent dilation of endothelium‐intact and surprisingly, endothelium‐denuded HAAs (% dilation at 10−5 M, 95.3 ± 1.4%, n=9 intact; 95.4 ± 2.6%, n=6 denuded HAAs), suggesting a vasomotor role for both endothelial and smooth muscle TRPV2 channels. In contrast, bath application of capsaicin (10−10 – 10−6 M) induced constriction of both endothelium‐intact and denuded HAAs at concentrations of 10−7 M (−55 ± 8%; n=5) and 10−6 M (−50.8 ± 12.9%; n=5). Moreover, capsaicin (10−6 M) induced a prolonged increase in intracellular calcium concentration ([Ca2+]i) in smooth muscle cells of HAAs, consistent with vasoconstriction observed in functional studies; whereas cannabidiol (10−7 – 10−5 M) induced a dose‐dependent increase in endothelial [Ca2+]i, consistent with vasodilation observed in functional studies. These results suggest that TRPV1 and TRPV2 channels are functionally expressed in human arterioles and upon activation, produce opposing vasomotor responses in HAAs. Further studies are required to determine the precise mechanisms responsible for such contrasting vasomotor effects of TRPV1 and TRPV2 activation.Support or Funding InformationSupport for this research was provided by the National Heart, Lung and BloodInstitute Grant R01‐HL 096647.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.