Plasmin is a proteolytic enzyme produced from plasminogen by plasminogen activators. We investigated the function of plasmin in human dental pulp fibroblast-like cells. Plasmin induced an increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)) in a concentration-dependent manner. Expression of mRNA for protease-activated receptor-1 (PAR-1) was detected, and the PAR-1 activating peptide SFLLRN induced an increase in [Ca(2+)](i) in the cells. The plasmin-induced increase in [Ca(2+)](i) was inhibited in the presence of the PAR-1 antagonist SCH79797. Plasmin stimulated the expression of interleukin-8 (IL-8) mRNA and prostaglandin E(2) release, which are involved in inflammation. These effects of plasmin on expression of IL-8 mRNA and prostaglandin E(2) release were inhibited in the presence of the PAR-1 antagonist SCH79797. These results suggest that plasmin activates PAR-1 and is involved in inflammation in human dental pulp. (C) 2008 Elsevier Inc. All rights reserved