| 12130703 |
Stenton GR, Nohara O, Dery RE, Vliagoftis H, Gilchrist M, Johri A, Wallace JL, Hollenberg MD, Moqbel R, Befus AD: Proteinase-activated receptor (PAR)-1 and -2 agonists induce mediator release from mast cells by pathways distinct from PAR-1 and PAR-2. J Pharmacol Exp Ther. 2002 Aug;302(2):466-74.
Because thrombin-induced inflammation is partially mast cell-dependent and involves proteinase-activated receptors (PARs), we hypothesized that mast cells express PAR and can be stimulated with PAR-activating peptides (PAR-AP). We demonstrated that rat peritoneal mast cells expressed PAR-1 and PAR-2 mRNA, and that PAR-2AP (tc-LIGRLO-NH (2), 1 microm) induced 64.2 +/- 4.4% specific beta-hexosaminidase release from peritoneal mast cells, whereas another PAR-2AP (SLIGRL-NH (2), 10 microM), trypsin (40 U/ml), and mast cell tryptase (1.5 microg/ml) did not. PAR-1AP (ApfFRChaCitY-NH (2), 10 microM) (Cit) induced 11.7 +/- 3.7% specific beta-hexosaminidase release, whereas another PAR-1AP (TFLLR-NH (2), 40 microM) and human thrombin (10 U/ml) did not. PAR-AP, tc-LIGRLO-NH (2), and Cit increased the free intracellular Ca (2+) concentration, whereas trypsin, tryptase, thrombin, and other PAR-APs did not. Desensitization of Ca (2+) flux with different agonists suggests that although tc-LIGRLO-NH (2), Cit, and compound 48/80 have similar mechanisms of action, tc-LIGRLO-NH (2) also activates mast cells by a mechanism distinct from that of 48/80. Using benzalkonium chloride, which antagonizes the actions of 48/80 by competing for the same G (i) protein, we determined that benzalkonium chloride suppressed tc-LIGRLO-NH (2)-mediated (0.1 microM) beta-hexosaminidase release by 62%. Moreover, removal of sialic acid from peritoneal mast cells, using neuraminidase (2 U/ml), inhibited Cit- (10 microM, 52%) and tc-LIGRLO-NH (2) (0.5 microM, 29%)-mediated beta-hexosaminidase release. Thus, tc-LIGRLO-NH (2) and Cit have at least partially similar mechanisms of action as 48/80. PAR-AP may therefore activate mast cells via multiple mechanisms that are distinct from those of classical PAR-1 and PAR-2. The responsiveness of mast cells to PAR-AP via a non-PAR-1/non-PAR-2 mechanism complicates the interpretation of in vivo studies using these peptides. |
34(0,1,1,4) |