In fura-2-loaded human periodontal ligament (HPDL) cells, bradykinin induced a rapidly transient increase and subsequently sustained increase in cytosolic Ca2+ ([Ca2+]i). When external Ca2+ was chelated by EGTA, the transient peak of [Ca2+]i was reduced and the sustained level was abolished, implying the Ca2+ mobilization consists of intracellular Ca2+ release and Ca2+ influx. Thapsigargin, a specific Ca2+-ATPase inhibitor for inositol 1,4,5-trisphosphate (1,4,5-1P3)-sensitive Ca2+ pool, induced an increase in [Ca2+]i in the absence of external Ca2+. After depletion of the intracellular Ca2+ pool by thapsigargin, the increase in [Ca2+]i induced by bradykinin was obviously reduced. Bradykinin also stimulated formation of inositol polyphosphates including 1,4,5-IP3. These results suggest that bradykinin stimulates intracellular Ca2+ release from the 1,4,5-1P3-sensitive Ca2+ pool. Bradykinin stimulated prostaglandin E2 (PGE2) release in the presence of external Ca2+, but not in the absence of external Ca2+. Ca2+ ionophore A23187 and thapsigargin evoked the release of PGE2 in the presence of external Ca2+ despite no activation of bradykinin receptors. These results indicate that bradykinin induces Ca2+ mobilization via activation of phospholipase C and PGE2 release caused by the Ca2+ influx in HPDL cells.