Abstract
Studies suggest that arteriolar pressure-induced vasoconstriction can be initiated by GPCRs (G protein-coupled receptors), including the AT(1)R (angiotensin II type 1 receptor). This raises the question, are such mechanisms regulated by negative feedback? The present studies examined whether RGS (regulators of G protein signaling) proteins in vascular smooth muscle cells are colocalized with the AT(1)R when activated by mechanical stress or angiotensin II and whether this modulates AT(1)R-mediated vasoconstriction. To determine whether activation of the AT(1)R recruits RGS5, an in situ proximity ligation assay was performed in primary cultures of cremaster muscle arteriolar vascular smooth muscle cells treated with angiotensin II or hypotonic solution in the absence or presence of candesartan (an AT(1)R blocker). Proximity ligation assay results revealed a concentration-dependent increase in trafficking/translocation of RGS5 toward the activated AT(1)R, which was attenuated by candesartan. In intact arterioles, knockdown of RGS5 enhanced constriction to angiotensin II and augmented myogenic responses to increased intraluminal pressure. Myogenic constriction was attenuated to a higher degree by candesartan in RGS5 siRNA-transfected arterioles, consistent with RGS5 contributing to downregulation of AT(1)R-mediated signaling. Further, translocation of RGS5 was impaired in vascular smooth muscle cells of spontaneously hypertensive rats. This is consistent with dysregulated (RGS5-mediated) AT(1)R signaling that could contribute to excessive vasoconstriction in hypertension. In intact vessels, candesartan reduced myogenic vasoconstriction to a greater extent in spontaneously hypertensive rats compared with controls. Collectively, these findings suggest that AT(1)R activation results in translocation of RGS5 toward the plasma membrane, limiting AT(1)R-mediated vasoconstriction through its role in G(q/11) protein-dependent signaling.