Human salivary gland cells express bradykinin receptors that modulate the expression of proinflammatory cytokines

Abstract

Bradykinin is an important peptide modulator that affects the function of neurons and immune cells. However, there is no evidence of the bradykinin receptors and their functions in human salivary glands. Here we have identified and characterized bradykinin receptors on human submandibular gland cells. Both bradykinin B1 and B2 receptors are expressed on human submandibular gland cells, A253 cells, and HSG cells. Bradykinin increased the intracellular Ca2+ concentration ([Ca2+](i)) in a concentration-dependent manner. Interestingly, a specific agonist of the B1 receptor did not have any effect on [Ca2+](i) in HSG cells, whereas specific agonists of the B2 receptor had a Ca2+ mobilizing effect. Furthermore, application of the B1 receptor antagonist, R715, did not alter the bradykinin-mediated increase in cytosolic Ca2+, whereas the B2 receptor antagonist, HOE140, showed a strong inhibitory effect, which implies that bradykinin B2 receptors are functional in modulating the concentration of cytosolic Ca2+. Bradykinin did not affect a carbachol-induced rise of [Ca2+](i) and did not modulate translocation of aquaporin-5. However, bradykinin did promote the expression of proinflammatory cytokines, including tumor necrosis factor- (TNF-), implying the role of bradykinin in salivary gland inflammation. These data suggest that bradykinin receptors are involved in Ca2+ signaling in human submandibular gland cells and serve a unique role, which is separate from that of other salivary gland G protein-coupled receptors.