PROTEINASE-ACTIVATED RECEPTOR-2 (PAR(2))-ACTIVATING PEPTIDES - IDENTIFICATION OF A RECEPTOR DISTINCT FROM PAR(2) THAT REGULATES INTESTINAL TRANSPORT

The effects of PAR(2)-activating PAR(2-)activating peptides, SLIGRL (S L)-NH2, and trans-cinnamoyl-LIGRLO (tc)-NH2 were compared with the act ion of trypsin, thrombin, and the PAR(1) selective-activating peptide: AlaparafluoroPhe-Arg-cyclohexylAla-Citrulline-Tyr (Cit)-NH2 for stimu lating intestinal ion transport. These agonists were added to the sero sa of stripped ratjejunum segments mounted in Ussing chambers, and sho rt circuit current (Isc) was used to monitor active ion transport. The relative potencies of these agonists also were evaluated in two bioas says specific for the activation of rat PAR(2): a cloned rat PAR(2) ce ll calcium-signaling assay (PAR(2)-KNRK cells) and an aorta ring relax ation (AR) assay. In the Isc assay, all agonists, except thrombin, ind uced an Isc increase, The SL-NH2-induced Isc changes were blocked by i ndomethacin but not by tetrodotoxin. The relative potencies of the ago nists in the Isc assay (trypsin >> SL-NH2 > tc-NH2 > Cit-NH2) were str ikingly different from their relative potencies in the cloned PAR(2)-K NRK cell calcium assay (trypsin >>>tc-NH2 congruent to SL-NH2 >>>Cit-N H2) and in the AR assay (trypsin >>>tc-NH2 congruent to SL-NH2). Furth ermore, all agonists were maximally active in the PAR(2)-KNRK( cell an d AR assays at concentrations that were one (PAR(2) -activating peptid es) or two (trypsin) orders of magnitude lower than those required to activate intestinal transport. Based on the distinct potency profile f or these agonists and the considerable differences in the concentratio n ranges required to induce an Isc effect in the intestinal assay comp ared with the PAR(2)-KNRK and AR assays, we conclude that a proteinase -activated receptor, pharmacologically distinct from PAR(2) and PAR(1) is present in rat jejunum and regulates intestinal transport via a pr ostanoid-mediated mechanism.