Abstract

Bradykinin produced at sites of tissue injury and inflammation elicits acute pain and alters the sensitivity of nociceptive neurons to subsequent stimuli. We tested the hypothesis that bradykinin could elicit long-lasting changes in nociceptor function by activating members of the nuclear factor of activated T-cells (NFAT) family of transcription factors. Bradykinin activation of B₂ receptors evoked concentration-dependent (EC₅₀ = 6.0 ± 0.3 nM) increases in intracellular Ca²⁺ concentration ([Ca²⁺]_i) in a proportion of dorsal root ganglion neurons in primary culture. These [Ca²⁺] increases were sensitive to inhibition of phospholipase C (PLC) and depletion of Ca²⁺ stores. In neurons expressing a green fluorescent protein (GFP)-NFAT4 fusion protein, a 2-min exposure to bradykinin induced the translocation of GFP-NFAT4 from the cytoplasm to the nucleus. Translocation was partially inhibited by the removal of extracellular Ca²⁺ and was blocked by inhibition of calcineurin. Furthermore, bradykinin triggered a concentration-dependent increase in NFAT-mediated transcription of a luciferase gene reporter (EC₅₀ = 24.2 ± 0.1 nM). This depended on the B₂ receptor, PLC activation, and inositol triphosphate-mediated Ca²⁺ release. Transcription was not inhibited by capsazepine. Finally, as indicated by quantitative reverse transcription-polymerase chain reaction, bradykinin elicited an increase in cyclooxygenase mRNA. This increase was sensitive to calcineurin and B₂ receptor inhibition. These findings suggest a mechanism by which short-lived bradykinin-mediated stimuli can enact lasting changes in nociceptor function and sensitivity.