Evidence that PAR-1 and PAR-2 mediate prostanoid-dependent contraction in isolated guinea-pig gallbladder

1 We have investigated the ability of protease-activated receptor-1 (PAR-1), PAR-2, PAR-3 and PAR-4 agonists to induce contractile responses in isolated guinea-pig gallbladder. Thrombin, trypsin, mouse PAR-1 activating (SFLLRN-NH₂) peptide, and mouse PAR-2 activating (SLIGRL-NH₂) and human PAR-2 activating (SLIGKV-NH₂) peptides produced a concentration-dependent contractile response. 2 Mouse PAR-4 activating (GYPGKF-NH₂ peptide, the mouse PAR-1 reverse (NRLLFS-NH₂) peptide, the mouse PAR-2 reverse (LRGILS-NH₂) and human PAR-2 reverse (VKGILS-NH₂) peptides caused negligible contractile responses at the highest concentrations tested. 3 An additive effect was observed following the contractile response induced by either trypsin or thrombin, with the addition of a different PAR agonist (SFLLRN-NH₂ and SLIGRL-NH₂, respectively). Desensitization to PAR-2 activating peptide attenuated the response to trypsin but failed to attenuate the response to PAR-1 agonists, and conversely desensitization to PAR-1 attenuated the response to thrombin but failed to alter contractile responses to PAR-2 agonists. 4 The contractile responses produced by thrombin, trypsin, SFLLRN-NH₂ and SLIGRL-NH₂ were markedly reduced in the presence of the cyclo-oxygenase inhibitor, indomethacin, whilst the small contractile response produced by NRLLFS-NH₂ and LRGILS-NH₂ were insensitive to indomethacin. 5 The contractile responses to thrombin, trypsin, SFLLRN-NH2 and SLIGRL-NH₂ were unaffected by the presence of: The non-selective muscarinic antagonist, atropine; the nitric oxide synthase inhibitor, L-NAME; the sodium channel blocker, tetrodotoxin; the combination of selective tachykinin NK₁ and NK₂ receptor antagonists, (S)-1-[2-[3-(3,4-dichlorphenyl)-1 (3-isopropoxyphenylacetyl) piperidin-3-yl] ethyl]-4-phenyl-1 azaniabicyclo [2.2.2] octane chloride (SR140333) and (S)-N-methyl-N-[4-acetylamino-4-phenylpiperidino-2-(3,4-dichlorophenyl)-butyl ] benzamide (SR48968), respectively. 6 The results indicate that PAR-1 and PAR-2 activation causes contractile responses in the guineapig gallbladder, an effect that is mediated principally by prostanoid release, and is independent of neural mechanisms.