Effect of bradykinin on intracellular signalling systems in a rat clonal dental pulp-cell line

The cloned pulp-cell line RDP4-1 increases cAMP production, hydrolyses phosphoinositide (PI) and mobilizes calcium in response to prostaglandin E2 (PGE2) and PGF2-alpha. The effect of bradykinin (BK) on intracellular signalling systems and DNA synthesis was studied in these cells. BK (10 microM) transiently increased cytoplasmic free calcium ([Ca2+]i) both in the presence and absence of external calcium. After stimulation with BK (10 microM), cells did not respond significantly to PGE2 (0.5 microgram/ml). Pretreatment with indomethacin (30 microM) inhibited the [Ca2+]i increment by BK (10 microM), but not by the subsequent addition of PGE2 (0.5 micrograms/ml). Also, pretreatment with PGE2 (0.5 microgram/ml) blocked the action of BK (10 microM), BK (0.1-100 microM) stimulated PI hydrolysis and cAMP production in a dose-dependent manner. Both the PI and the cAMP responses were inhibited by indomethacin (30 microM), as was the calcium response. BK (0.01-10 microM) also stimulated release of arachidonic acid and its metabolites dose-dependently. However, prolonged exposure to BK in serum-deficient medium did not exert any effect on DNA synthesis. RDP 4-1 cells, therefore, appear to respond to BK with increased cAMP production. PI hydrolysis and calcium mobilization. The inhibition of these effects of BK by indomethacin raises the possibility that cyclo-oxygenase product(s), especially PGE2 or PGE2-like compounds, may be responsible for evoking these effects. These results indicate that BK may stimulate or modulate cell metabolism in the dental pulp.