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

Proteinase-activated 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 muM) 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 muM 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.