The N B method has the overall advantage that it
The N&B method has the overall advantage that it is not restricted to certain dyes specific for energy transfer , and is also able to detect higher order receptor Cy7 NHS ester on the focal point in living cells.
Conclusion The N&B method has shown to be a powerful tool to locate and quantify the aggregation state of the AT1 and the ETA receptors on the plasma membrane in living cells. The present study showed evidence that the AT1 and the ETA receptors were not expressed near or on the plasma membrane as monomers, but also as possibly constitutive dimers and tetramers. For both receptors, the proportion of monomers, dimers and tetramers were unaffected by their respective agonist binding. Same situation was seen by the selective ETA receptor antagonist sitaxentan.
Conflict of interest
Acknowledgments The authors gratefully acknowledge the National Secretariat for Science, Technology and Innovation (SENACYT) of the Republic of Panama for financial support to Dr. Caballero-George and Ms. Planes through the incentive program of the National Investigation System (SNI). Also to Dr. Caballero-George through grant COL10-070, additionally to Ms. Planes through grant No. 172-2016. Moreover, thanks to IFARHU from the Panamanian government, which jointly with SENACYT gave a scholarship to Ms. Planes. The authors wish to thank Hongtao Chen for the assistance on the TIRF microscope setup and Maria Beatriz Carreira for helping with the statistical analysis. Dr. Gratton and Dr. Digman acknowledge support from Grants NIH P41-GM103540 and NIH P50-GM076516.
Introduction Endothelins (ETs) are a family of multifunctional, naturally occurring peptides with long-lasting vasoconstrictor and pressor effects (Zhou et al., 2004). They are synthesized as a large protein, the pre-proET-1 or Big ET-1, which is subsequently cleaved to pro-ET-1 and then ET-1 by ET-converting enzymes (Thorin and Webb, 2010). ETs comprise three isoforms: ET-1, ET-2 and ET-3. Among these, ET-1 is the most active and dominant form and seems to play a vital role in cardiovascular regulation. ET-1 is synthesized mainly in endothelial cells and is released and interacts with the vascular smooth muscle. ET-1 is also synthesized in vascular smooth muscle cells as well as in extravascular tissues such as the spleen, pancreas, lung, nervous system, and kidneys (Bourque et al., 2011). ET-1 is released continuously from endothelial cells by constitutive and regulated machinaries, producing intense constriction of the underlying smooth muscle and contributing to the maintenance of endogenous vascular tone. ET-1 exerts its effects via activating two G-protein-coupled ET receptors, designated as ETA and ETB (Kohan et al., 2011). This review sums up recent evidence regarding the potential use of ET receptor blockers in the management of cardiovascular disease, with more emphasis on selective ETA receptor antagonism.
Cardiovascular and renal effects of ET-1 ET-1 produces positive chronotropic and inotropic effects (Kedzierski and Yanagisawa, 2001). In the vascular system, ETA receptors are predominantly found in vascular smooth muscle cells and its activation leads to vasoconstriction. In contrast, ETB receptors are highly expressed in the endothelium as well as in vascular smooth muscle cells (Kohan et al., 2011). Whereas ETB receptors present in smooth muscle mediate vasoconstriction, those in endothelial cells cause vasodilation via facilitating the generation of NO and prostacyclin (Zhou et al., 2004, Bourque et al., 2011). However, the precise vascular effects of ET-1 depend on the animal species and vascular bed. In some blood vessels such as the rabbit saphenous vein, rabbit jugular vein, rat renal vascular bed, and porcine pulmonary vein, ETB receptors mediate vasoconstriction. In other vessels, ET-1 is thought to mediate vasoconstriction via the activation of both receptors (Davenport, 2002). In the kidney, ETs play a major role in the renal control of water and sodium excretion and the modulation of the total and regional blood flow and glomerular filtration rate (Chade et al., 2014). Although ET-1 causes equal constriction of afferent and efferent arterioles in vitro, the efferent arterioles are the predominant site of action of endogenous ET-1 (Agapitov and Haynes, 2002).