PAR-2 elicits afferent arteriolar vasodilation by NO-dependent and NO-independent actions

Abstract

vated receptors (PARs) are a novel class of G protein-coupled receptors that respond to signals through endogenous proteinases. PAR activation involves enzymatic cleavage of the extracellular NH2-terminal domain and unmasking of a new NH2 terminus, which serves as an anchored ligand to activate the receptor. At least four PAR subtypes have been identified. In the present study, we used the in vitro perfused hydronephrotic rat kidney to examine the effects of activating PAR-2 on the afferent arteriole. The synthetic peptide SLIGRL-NH2, which corresponds to the exposed ligand sequence and selectively activates PAR-2, did not alter basal afferent arteriolar diameter but caused a concentration-dependent vasodilation (3-30 M) of arterioles preconstricted by angiotensin II (0.1 nM). A modified peptide sequence (LSIGRL-NH2, inactive at PAR-2) had no effect. This vasodilation was characterized by an initial transient component followed by a smaller sustained response. A similar pattern of vasodilation was seen when SLIGRL-NH2 was administered to isolated perfused normal rat kidney. The sustained component of the PAR-2-induced afferent arteriolar vasodilation was eliminated by nitric oxide (NO) synthase inhibition (100 M nitro-L-arginine methyl ester). In contrast, the transient vasodilation persisted under these conditions. This transient response was not observed when afferent arterioles were preconstricted with elevated KCl, suggesting involvement of an endothelium-derived hyperpolarizing factor. Finally, RT-PCR revealed the presence of PAR-2 mRNA in isolated afferent arterioles. These findings indicate that PAR-2 is expressed in the afferent arteriole and that its activation elicits afferent arteriolar vasodilation by NO-dependent and NO-independent mechanisms.

Redundant signaling mechanisms contribute to the vasodilatory response of the afferent arteriole to proteinase-activated receptor-2

“…Each vasodilator elicited a transient response under the latter conditions and, in each case, the peak dilations were similar to the peak responses seen in controls. Moreover, these transient dilations were fully blocked by elevated extracellular K ϩ (16,41,44), consistent with the possible involvement of an EDHF. A common feature of all three agents was that a component of the dilation was blocked by treatment with apamin plus charybdotoxin (Figs.…”

“…These characteristics are similar to responses attributed to EDHF in other preparations (21,29,33,41). There is limited information on the nature of the EDHF involved in the responses of other vessel types to PAR-2 agonists.…”

“…As shown in the tracing depicted in The persistence of a transient vasodilatory response to PAR-2 activation in the presence of NOS and COX blockade is consistent with previous reports. We had previously shown that this NO-independent component is blocked by KCl-induced depolarization (41), and others have attributed such responses to an EDHF (15,29,30). We have observed NOindependent afferent arteriolar responses to both acetylcholine and bradykinin that exhibit similar temporal characteristics (43,44).…”

“…However, PAR-2 is also highly expressed in renal vascular endothelial cells and vascular smooth muscle cells (2). Previous studies from our laboratory using the isolated perfused rat kidney model (15) and the in vitro perfused hydronephrotic rat kidney preparation (41) have demonstrated a potential role for PAR-2 in the regulation of renal hemodynamics, as PAR-2 activation in these preparations exerts a potent renal vasodilatory response.…”

“…Both trypsin and the selective PAR-2-activating peptide SLIGRL-NH 2 induce endothelium-dependent vasodilation in isolated rat aorta, mouse mesenteric, and renal arteries (21,29,39). In some vessels, but not all, a component of the endothelium-dependent response is resistant to treatment with cyclooxygenase (COX) and nitric oxide synthase (NOS) inhibition, prompting speculation that PAR-2 activation causes the release of an endothelium-derived hyperpolarizing factor (EDHF) (15,21,29,30,41). In the isolated, perfused rat kidney, both SLIGRL-NH 2 and trypsin elicit renal vasodilation that is only partially attenuated by COX and NOS inhibition (15).…”