The protease-activated receptor-2 (PAR-2) has been implicated in airway inflammation. Here, we examined the interaction between PAR-2 and lipopolysaccharide (LPS), a major proinflammatory factor, using cultured guinea pig tracheal epithelial cells. In fura2-loaded cells, LPS (1 µg/ml) transiently increased intracellular Ca²⁺ concentrations ([Ca²⁺]i), this effect being abolished by a Ca²⁺ channel blocker, verapamil and Ca²⁺ removal. Prestimulation of PAR-2 with trypsin (0.1-1 U/ml) or an agonist peptide (SLIGRL-NH₂, 1 µM) for 60 min inhibited the LPS-induced [Ca²⁺]i increase. Such an inhibitory effect of trypsin was abolished by inhibitors of protein kinase C (PKC), chelerythrine and staurosporine. A PKC activator, phorbol 12, 13-dibutylate also reduced the LPS response. Trypsin also inhibited a transient increase in [Ca²⁺]i caused by a Ca²⁺ channel openner, Bay K 8644. When the trypsin-pretreated cells were incubated in normal buffer for 10-60 min prior to LPS exposure, the effect of trypsin on the Ca²⁺ response to LPS diminished in a time-dependent manner. Such a recovery was slowed by incubation with a protein phosphatase inhibitor, okadaic acid. Further, Trypsin induced sustained activations of PKC and -. Thus, PAR-2 stimulation reduced the epithelial cell response to LPS probably through the inactivation of Ca²⁺ channels via PKC-mediated phosphorylation.