Functional TRPV1 expression was observed in the arteriolar smooth muscle cells. We investigated functional expression of TRPV1 in various vascular tissues of the rat.

Methods: 

Wistar Kyoto (WKY) rats were used in immunohistochemical experiments where six anti-capsaicin receptor antibodies (Calbiochem N-term., Alomone C-term., Alomone 3rd loop, Osense 3rd loop, Osense 4th loop, Neuromics N-term) were tested. Isolated arterioles (musculus gracilis, mesenterium), coronary arterioles, carotis, aorta and femoral arterioles were tested in the functional measurements by capsaicin (specific agonist of TRPV1).

Results: 

Immunhistochemical results suggested that the expression of TRPV1 in dorsal root ganglion showed specific staining in the case of two antibodies (Calbiochem N-term., Alomone C-term.). Of these, the Calbiochem antibody showed specific staining in vascular smooth muscle cells of skeletal muscle, mesenteric sections, skin, carotis, aorta and coronary arterioles although the immunostaining of TRPV1 in vascular tissues was not homogeneous. Moreover, functional experiments suggest that the TRPV1 stimulation lead to constriction in the case of TRPV1 positive arteries. Nevertheless, capsaicin was ineffective in some arteries, where TRPV1 expression was detected by immunostaining. In particular, capsaicin (1 mM) evoked arteriolar constrictions in gracilis arterioles (decrease in diameter: from 194±11 mm to 39±3 mm, n=5), coronary arterioles and carotis, while no change in arteriolar diameter was found in mesenteric arterioles (diameter: from 395±22 mm to 400±26 mm, n=5), in aorta (contractile force: from 8,3±1,14 mN to 8,73±1,38 mN, n=4) and in femoral arterioles upon capsaicin treatment.

Our results suggest that TRPV1 is widely expressed in the mammalian vasculature, where its activation affects arteriolar diameter. Nonetheless, TRPV1 expression is not homogenous and TRPV1 sensitivity to its agonist (capsaicin) is regulated.