Changes in Inositol 1,4,5‐Trisphosphate and Inositol 1,3,4,5‐Tetrakisphosphate Mass Accumulations in Cultured Adrenal Chromaffin Cells in Response to Bradykinin and Histamine

Abstract: In previous studies it has been shown that both bradykinin and histamine increase the formation of ³H‐labeled inositol phosphates in adrenal chromaffin cells prelabelled with [³H]inositol and that both these agonists stimulate release of catecholamines by a mechanism dependent on extracellular calcium. Here, we have used mass assays of inositol 1,4,5‐trisphosphate [Ins(1,4,5)P₃] and inositol 1,3,4,5‐tetrakisphosphate [Ins(1,3,4,5)P₄] to investigate changes in levels of these two candidates as second messengers in response to stimulation with bradykinin and histamine. Bradykinin increased the mass of Ins(1,3,4,5)P₄ despite the failure in earlier studies with [³H]inositol‐labelled cells to observe a bradykinin‐mediated increase in content of [³H]InsP₄. Bradykinin elicited a very rapid increase in level of Ins(1,4,5)P³, which was maximal at 5–10 s and then rapidly decreased to a small but sustained elevation at 2 min. The bradykinin‐elicited Ins(1,3,4,5)P₄ response increased to a maximum at 30–60 s and at 2 min was still elevated severalfold above basal levels. Histamine, which produced a larger overall total inositol phosphate response in [³H]inositol‐loaded cells, produced significantly smaller Ins(1,4,5)P³ and Ins(1,3,4,5)P₄ responses compared with bradykinin. The bradykinin stimulation of Ins(1,4,5)P₃ accumulation was partially dependent on a high (1.8 mM) extracellular Ca₂₊ concentration, whereas the Ins(1,3,4,5)P₄ response was almost completely lost when the extracellular Ca²⁺ concentration was reduced to 100 nM. Changes in the inositol polyphosphate second messengers are compared with the time course of bradykinin‐stimulated increases in free intracellular Ca²⁺ concentrations and noradrenaline release.