Ion transport regulated by protease-activated receptor 2 in human airway Calu-3 epithelia

1 We examined the mechanisms underlying anion secretion mediated by protease-activated receptor 2 (PAR2) and its role in the regulation of ion transport, using polarized human airway Calu-3 cells. 2 PAR2 stimulation by trypsin and a PAR2-activating peptide (PAR2AP), especially from the basolateral aspect, caused transient Cl- secretion due to cytosolic Ca2+ mobilization. 3 Antagonists of PI-PLC (U73122, ET-18-OCH3) and inositol 1,4,5-triphosphate (xestospongin C (Xest C)) were without effect on thePAR2AP- mediated Cl- secretion, whereas it was attenuated by D609 ( a PC-PLC inhibitor) and phorbol 12-myristate 13 acetate (PMA, a PKC activator). 4 Even 30 min after removal of PAR2AP after a 10-min-exposure, cells were still poorly responsive to PAR2 stimulation, but the reduced responsiveness was upregulated by a PKC inhibitor, GF109203X (GFX). 5 Pretreatment with PAR2AP did not affect responses to anion secretagogues, such as isoproterenol, forskolin, thapsigargin, 1-ethyl-2-benzimdazolinone, and adenosine, but ATP-induced responses were significantly reduced. Nystatin permeabilization studies revealed that the presence of PAR2AP prevented ATP-induced increments in basolateral membrane K+ conductance without affecting apical membrane Cl- conductance. 6 ATP-elicited Ca2+ mobilization, which was sensitive to D609 and PMA, was inhibited by the pretreatment with PAR2AP, and this inhibition was blunted by the presence of GFX. 7 Collectively, stimulation of PAR2 generates a brief response of Cl- secretion through PC-PLC-mediated pathway, followed by not only auto-desensitization of PAR2 itself but also cross-desensitization of a PC-PLC-coupled purinoceptor. The two types of desensitization seem likely to have PKC-mediated downregulation of PC-PLC in common.