[show abstract][hide abstract] ABSTRACT: N ociceptors are a group of neurons with afferent (sensorial) and efferent (motor) functions related to pain. These nociceptors participate in the regulation of vascular tone, cardiac functions, immu-nological processes and tisse growth, among other functions, in response to mechanical and thermal stimuli (1-4). Activation of noci-ceptors induces the release of neuropeptides, such as substance P, neurokinin-A, the calcitonin gene-related peptide (CGRP), soma-tostatin and others (3-5). CGRP is a cardiotonic agent dependent on nitric oxide (NO) production (5). NO is produced in almost all tissues and organs, exerting a variety of biological actions under both physi-ological and pathological conditions (5). NO mediates vascular relaxation by increasing the levels of cyclic GMP and cyclic AMP in smooth muscle cells. NO release can be stimulated by sarcolemmal hyperpolarization and increased Ca 2+ permeability (6) with the consequent activation of the endothelial NO synthase (NOS)-3 (7-10). In addition, during hypertension in humans and in animal models of salt-sensitive hypertension, CGRP exhibits important vasodilator actions, decreasing blood pressure through interactions with NO (11-16). Release of neuropeptides from nociceptors is also caused by activation of a member of the transient receptor potential (TRP) receptors subfamily, known as the vanilloid type 1 receptor (VR1) or the TRPV1 receptor, which is present in nociceptors (17-19). The TRPV1 receptor has also been described in endothelial cells of human pulmonary and cerebral arteries (18). The presence of the TRPV1 receptor has been suggested in other vascular regions as well (20-22). The TRPV1 receptor is sensitive to capsaicin (8-methyl-vannillyl-6-noneamide) which is a neurotoxin obtained from plants of the genus Capsicum (chili pepper) that has been used as an analgesic in diverse pain-related pathologies. This alkaloid, as well as its antagonist capsazepine, have been used as tools to study the structure and function of the TRPV1 receptor, which is an integral membrane protein (23-25). The TRPV1 receptor is also activated by cannabinoid substances, such as anandamide and 2-arachidonoyl-glycerol (26,27), which causes important vasodilator effects attributed to the actions of CGRP and NO (11-16,18,19). The mechanisms modulating NO release in the endothelium are multifactorial. Shear stress generated by blood flow is well known to physiologically regulate NO release (28,29). Regulation of Ca 2+ flux in the endothelium is mediated by at least one type of channel that is sensitive to mechanical stress, the stretch-activated ion channels (SACs) (30-32). SACs are functionally characterized; however, the molecular structure of SACs is not known. The TRPV1 receptor and SACs share functional characteristics including their sensitivity to mechanical stimuli and their selectivity to ions such as Na + , Ca 2+ and K + (24,30). SACs have been studied in the examination of Ca 2+ currents in Xenopus cells, where it was found that the activity of this type of SAC can be blocked with the trivalent lanthanide gadolin-ium (Gd 3+), thereby inhibiting the generation of NO dependent on NOS-3 activation (33-35). The role of the TRPV1 receptor and SACs in NO release in the heart or in the aorta has only been partially explored. We hypothesized that there are functional similarities between SACs and the TRPV1 receptor. Therefore, we explored the functional similarities between the TRPV1 receptor and SACs on NO release in the heart, in the thoracic aorta (TA) and in endothelial cells in culture.
Experimental and clinical cardiology 01/2012; 17:89. · 1.10 Impact Factor
[show abstract][hide abstract] ABSTRACT: Shear stress stimulates nitric oxide (NO) release in endothelial cells. Stretch-activated ion channels (SACs) and the transient receptor potential vanilloid type 1 (TRPV1) receptor respond to mechanical stimulus and are permeable to Na(+), Ca(2+) and K(+). The influence of SACs and the TRPV1 receptor on NO release on the heart and on the vascular reactivity of the thoracic aorta (TA) was studied. Experiments were performed in isolated perfused heart, cultured endothelial cells and TA rings from Wistar rats. Capsaicin (10 μM, 30 μM) was used as a NO release stimulator, capsazepine (6 μM, 10 μM) was used as a capsaicin antagonist and gadolinium (3 μM, 5 μM) was used as an inhibitor of SACs. NO was measured by the Kelm and Tenorio methods. Left ventricular pressure was recorded and coronary vascular resistance was calculated. Capsaicin increased NO release in the heart by 58% (395±8 pmol/mL to 627±23 pmol/mL). Capsazepine and gadolinium inhibited NO release by 74% and 82%, respectively. This tendency was similar in all experimental models. Capsaicin attenuated the effects of norepinephrine (10 M to 7 M) on TA and had no effect in the presence of N (ω)-nitro-L-arginine methyl ester. Therefore, the authors conclude that SACs and the TRPV1 receptor are both present in the coronary endothelium and that both participate in Ca(2+)-dependent NO release.
Experimental and clinical cardiology 09/2012; 17(3):89-94. · 1.10 Impact Factor
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