Regulation of calcium homeostasis in sensory neurons by bradykinin

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Abstract
The nonapeptide bradykinin (BK) activates sensory neurons and stimulates the transmission of nociceptive information into the CNS. We investigated the effect of this peptide on rat dorsal root ganglion neurons (DRG) grown in vitro. BK stimulated the synthesis of inositol trisphosphate (IP3) and the breakdown of phosphatidylinositol bisphosphate, the synthesis of diacylglycerol, and the release of arachidonic acid from DRG cells. The release of IP3 and arachidonic acid was not inhibited by pretreatment of the cells with pertussis toxin. BK also mobilized intracellular Ca2+ stores in DRG cells as assessed by fura-2-based microfluorimetry. Two types of Ca2+ stores appeared to exist in DRG neurons. One type could be mobilized by caffeine (10(-2) M), and this effect could be blocked by ryanodine in a use-dependent manner. These stores occurred primarily in the cell soma and were virtually absent from cell processes. A second type of store could be mobilized by BK, presumably through the mediation of IP3. These latter stores were distributed equally between the cell soma and processes. Experiments with combinations of caffeine and BK suggested that the stores mobilized by these 2 agents may be separate entities. Both the caffeine and BK sensitive Ca2+ storage sites appeared to participate in buffering a Ca2+ load induced in DRG neurons by cell depolarization. The relevance of these observations to the mechanism of action of BK on sensory neurons is discussed.