The role of protease-activated receptor-2 (PAR2) in the modulation of beating of the mouse isolated ureter: lack of involvement of mast cells or sensory nerves

1 The localization of protease-activated receptor-2 (PAR2) and the effects of PAR:! activators were investigated in the mouse isolated ureter in order to test the hypothesis that PAR2 activation may initiate neuropeptide rele ase from sensory nerve fibres and hence contribute to inflammation. 2 PAR2 was localized by fluorescence immunohistochemistry to both the smoot h muscle and epithelium of the meter. Macrophage-like cells in the adventit ia of the ureter were also PAR2 immunoreactive. PAR2-immunoreactivity was n ot observed in mast cells or nerve fibres. 3 In circular muscle preparations of the ureter in which continuous rhythmi c beating was induced by KCl (20 mM) and the thromboxane A(2) mimetic U4661 9 (0.3 mu M), trypsin (0.3 U ml(-1)) reduced beat frequency to 84.6 +/- 2.0 % of control rates. The PAR2-selective peptide agonist SLIGRL-NH2 concentra tion-dependently (0.1 - 3.0 mu M) slowed beat frequency to a maximum of 72. 7 +/- 2.0%. 4 Histamine (1-300 mu M) was more efficacious than SLIGRL-NH2 in inhibiting ureter beat frequency in a concentration-dependent manner to a maximum (at 300 mu M) of 7.9 +/- 2.5% of the control rate. 5 Pretreatment of preparations with capsaicin (10 mu M for 30 min) markedly attenuated the inhibitory effect of histamine, but not that of SLIGRL-NW2, indicating a role for sensory nerves in the inhibitory effect of histamine only. 6 The inhibitory effect of SLIGRL-NH2 on ureter beat Frequency was unaffect ed by the nitric oxide (NO) synthase inhibitor, L-NOARG (100 mu M) or the c yclo-oxygenase inhibitor, indomethacin (3 mu M). 7 In conclusion, PAR2 activation causes inhibition of beating in the mouse ureter that is not mediated by axon reflex release of inhibitory neuropepti des. This inhibitory effect of PAR2 appears to be mediated directly on smoo th muscle cells, although the contribution of non-NO, non-prostanoid epithe lium-derived factors cannot be ruled out.