Characterization of TRPV1 and TRPV2 channel expression and vasomotor function in human arterioles

Transient receptor potential vanilloid (TRPV) channels, act as sensory mediators and are activated by endogenous ligands, heat, mechanical and osmotic stress. Within the vasculature, TRPV channels are expressed in smooth muscle cells, endothelial cells and in perivascular nerves. We have previously demonstrated that Ca 2+ influx through endothelial TRPV4 channels mediates flow‐induced dilation (FID) of human coronary arterioles (HCA) from subjects with coronary artery disease (CAD). Other studies have also implicated endothelial TRPV1 channels in FID, whereas a functional role for endothelial TRPV2 channels has yet to be determined. Recent unpublished studies from our lab showed that FID was not affected by TRPV4 inhibition in HCA from subjects without CAD (non‐CAD). Instead, inhibition of TRPV1 or TRPV2 reduced FID of HCA from non‐CAD subjects. Collectively, these data have led us to hypothesize that different TRPV channels contribute to FID of arteries from non‐CAD vs CAD subjects, with TRPV4 prominent in CAD vessels and TRPV1/2 more important in non‐CAD vessels. The objective of the current study was to characterize the expression and function of TRPV1 and TRPV2 channels in HCA and human adipose arterioles (HAA) from non‐CAD subjects, using molecular, immunological and vascular reactivity studies. We first examined TRPV1 and TRPV2 mRNA expression in HCA and HAA using RT‐PCR and consistently detected both transcripts in multiple samples. As a positive control, human brain tissue was found to express TRPV1 and TRPV2 transcripts. Consistent with mRNA expression, TRPV1 and TRPV2 proteins were detected in membrane fractions of HCA and HAA using western blot analysis. Antibody specificity was confirmed in TRPV1 or TRPV2 transfected versus non‐transfected HEK‐293 cells. We next examined the vasomotor effect of capsaicin, a selective TRPV1 agonist and cannabidiol, a selective TRPV2 agonist on freshly isolated HAA. HAA (100–200 μm), obtained from subjects without CAD, were cannulated under 60 mmHg and examined for diameter changes using videomicroscopy. Surprisingly, bath application of capsaicin induced constriction of HAA at concentrations of 10 −7 M and 10 −6 M (−46.82 ± 4.3%; n=3), with no significant effect at lower concentrations (10 −10 –10 −8 M). In contrast, cannabidiol (10 −6 ,10 −5 ,3×10 −5 M) induced a dose‐dependent dilation of HAA. These results suggest that TRPV1 and TRPV2 channels are expressed in human arterioles and contribute to vasomotor responses. Further studies are required to determine the specific role of the endothelium versus smooth muscle and perivascular nerves, in mediating the vascular responses to TRPV1 and TRPV2 activation. Support or Funding Information Support for this research was provided by the National Heart, Lung and Blood Institute Grant R01‐HL 096647