A23187, free acid

A23187, free acid is a Ca2+ ionophore [1].

Ca2+ ionophore acts as a Ca2+ ionophore, allowing Ca2+ to cross cell membranes.

A23187, free acid is a Ca2+ ionophore. In rat Kupffer cells, A23187 induced hydrolysis of phosphoinositides to inositol phosphates and released inositol phosphates from the cells in a concentration- and time-dependent way [1]. In HL-60 cells, A23187 increased intracellular Ca2+ levels. Also, A23187 generated reactive oxygen species (ROS) both in intracellular and extracellular and induced apoptotic cell death, which was dependent on mitochondrial permeability transition [2]. In ileal muscle, A23187 (10-5 M) induced initial contraction and small rhythmic contractions with decrease in phosphocreatinine (PCr), ATP and glycogen contents under hypoxic conditions. However, A23187 (10-5 M) induced initial contraction and successive rhythmic contractions with a significant decrease in the ATP and glycogen contents in glucose-free medium [3]. In rat C6 glioma cells that was resistant to ZnCl2 (250 μM), A23187 (100 nM) and Zn2+ (150 μM) significantly induced apoptosis. Also, A23187 (1.9 nM) significantly increased the intracellular mobile Zn2+ content. These results suggested that the apoptosis induced by Zn2+ and A23187 was the result of increased Zn2+ influx induced by A23187 [4].

References:
[1].  Gandhi CR, Harvey SA, Cevallos M, et al. A23187 causes release of inositol phosphates from cultured rat Kupffer cells. Eur J Pharmacol, 2001, 415(1): 13-18.
[2].  Kajitani N, Kobuchi H, Fujita H, et al. Mechanism of A23187-induced apoptosis in HL-60 cells: dependency on mitochondrial permeability transition but not on NADPH oxidase. Biosci Biotechnol Biochem, 2007, 71(11): 2701-2711.
[3].  Nasu T, Nishikawa M. Metabolic dependency of ionophore A23187-induced contraction of ileal longitudinal smooth muscle. J Auton Pharmacol, 2000, 20(2): 99-109.
[4].  Jansen S, Arning J, Beyersmann D. Effects of the Ca ionophore a23187 on zinc-induced apoptosis in C6 glioma cells. Biol Trace Elem Res, 2003, 96(1-3): 133-142.

Epidermal growth factor (EGF), tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) and calcium ionophore A23187 increase cytoplasmic free calcium and stimulate arachidonic acid release and PGE2/6-keto PGF1 alpha production in cultured porcine thyroid cells.[Pubmed:3121392]

FEBS Lett. 1987 Dec 10;225(1-2):43-7.

Epidermal growth factor (EGF), 12-O-tetradecanoylphorbol 13-acetate (TPA) and calcium ionophore A23187 increase cytoplasmic free calcium ([Ca2+]i) and stimulate arachidonic acid release and production of PGE2 and 6-keto PGF1 alpha, an end metabolite of PGI2, in cultured porcine thyroid cells. Addition of EGF, TPA or A23187 to the cells loaded with fura-2, a fluorescent Ca2+ indicator, causes an immediate increase in [Ca2+]i, which is the earliest event after mitogen stimulation. This [Ca2+]i response occurs immediately, reaching a maximum within several seconds. EGF, TPA and A23187 stimulate arachidonic acid release and PGE2 and 6-keto PGF1 alpha production; the maximum effects are obtained after 2-4 h incubation. EGF, TPA and A23187 increase [Ca2+]i and then stimulate arachidonic acid release and PG production.

Ionophore A23187. Solution conformations of the calcium complex and free acid deduced from proton and carbon-13 nuclear magnetic resonance studies.[Pubmed:764856]

Biochemistry. 1976 Jan 13;15(1):132-41.

Proton and carbon-13 nuclear magnetic resonance (NMR) spectra have been used to deduce possible biologically relevant conformations of ionophore A23187 as the free acid, and as the calcium complex, in solution. By analysis of coupling constants and dihedral angles obtained from 270-MHz proton NMR, A23187 free acid molecules and individual A23187 anions which comprise the calcium complex are found to differ principally by the rotational state of a carbon-carbon single bond near the benzoxazole ring. Proton Tl relaxation data and measurements of rotational correlation times confirm the dimeric nature of the calcium complex vs. the free acid monomer. Using the deduced pseudocyclic conformation for the A23187 anion, in conjunction with model-building studies, a conformation for the calcium complex is proposed, in which the benzoxazole carboxylate oxygen, the ketopyrrole oxygen, and the benzoxazole (ring) nitrogen atom of each molecule are the major participants in calcium binding. Additional stabilization of the structure is possible through the formation of a postulated hydrogen bond bridge between the pyrrole NH proton and benzoxazole carboxylate oxygen.

Zn(2+), derived from cell preparation, partly attenuates Ca(2+)-dependent cell death induced by A23187, calcium ionophore, in rat thymocytes.[Pubmed:19124067]

Toxicol In Vitro. 2009 Mar;23(2):338-45.

A23187, a calcium ionophore, is used to induce Ca(2+)-dependent cell death by increasing intracellular Ca(2+) concentration ([Ca(2+)](i)) under in vitro condition. Since this ionophore also increases membrane permeability of metal divalent cations such as Zn(2+) and Fe(2+) rather than Ca(2+), trace metal cations in cell suspension may affect Ca(2+)-dependent cell death induced by A23187. Therefore, the effects of chelators for divalent metal cations, EDTA and TPEN, on the A23187-induced cytotoxicity were cytometrically examined in rat thymocytes. The cytotoxicity of A23187 was attenuated by 1mM EDTA while it was augmented by 50 microM EDTA and 10 microM TPEN. These changes were statistically significant. The A23187-induced increase in Fluo-3 fluorescence intensity, a parameter for [Ca(2+)](i), was significantly reduced by 1mM EDTA while it was not the case for 50 microM EDTA and 10 microM TPEN. The intensity of FluoZin-3 fluorescence, a parameter for [Zn(2+)](i), increased by A23187 was respectively reduced by 50 microM EDTA and 10 microM TPEN. It is suggested that the attenuation of A23187-induced cytotoxicity by 1mM EDTA is due to the chelation of extracellular Ca(2+) and Zn(2+) while the augmentation by 50 microM ETDA or 10 microM TPEN is due to the chelation of extracellular Zn(2+). The Tyrode's solution without thymocytes contained 32.4 nM of zinc while it was 216.9 nM in the cell suspension. In conclusion, trace Zn(2+), derived from cell preparation, partly attenuates the Ca(2+)-dependent cell death induced by A23187.

Differential effects of endoplasmic reticulum stress-induced autophagy on cell survival.[Pubmed:17135238]

J Biol Chem. 2007 Feb 16;282(7):4702-10.

Autophagy is a cellular response to adverse environment and stress, but its significance in cell survival is not always clear. Here we show that autophagy could be induced in the mammalian cells by chemicals, such as A23187, tunicamycin, thapsigargin, and brefeldin A, that cause endoplasmic reticulum stress. Endoplasmic reticulum stress-induced autophagy is important for clearing polyubiquitinated protein aggregates and for reducing cellular vacuolization in HCT116 colon cancer cells and DU145 prostate cancer cells, thus mitigating endoplasmic reticulum stress and protecting against cell death. In contrast, autophagy induced by the same chemicals does not confer protection in a normal human colon cell line and in the non-transformed murine embryonic fibroblasts but rather contributes to cell death. Thus the impact of autophagy on cell survival during endoplasmic reticulum stress is likely contingent on the status of cells, which could be explored for tumor-specific therapy.

Platelet particle formation by anti GPIIIa49-66 Ab, Ca2+ ionophore A23187, and phorbol myristate acetate is induced by reactive oxygen species and inhibited by dexamethasone blockade of platelet phospholipase A2, 12-lipoxygenase, and NADPH oxidase.[Pubmed:17545506]

Blood. 2007 Sep 15;110(6):1989-96.

An HIV antibody (Ab) against platelet integrin GPIIIa49-66 induces complement-independent platelet particle formation by the elaboration of reactive oxygen species (ROS) downstream of the activation of the platelet NADPH oxidase by the 12-lipoxygenase (12-LO) product 12(S)-HETE. To determine whether other inducers of platelet particle formation also function via the induction of ROS, we examined the effects of the Ca(2+) ionophore A23187 and phorbol myristate acetate (PMA). Both agents induced oxidative platelet particle formation in an identical fashion as Ab, requiring Ca(2+) flux and 12(S)-HETE production as well as intact NADPH oxidase and 12-LO pathways. Since HIV-ITP patients with this Ab correct their platelet counts with dexamethasone (Dex), we examined the role of this steroid in this unique autoimmune disorder. Dex at therapeutic concentrations inhibited Ab-, A23187-, or PMA-induced platelet particle formation by inhibiting platelet PLA(2), 12-LO, and NADPH oxidase. The operational requirement of translocation of PLA(2), 12-LO, and NADPH oxidase components (p67 phox) from cytosol to membrane for induction of ROS was both inhibited and partially reversed by Dex in platelets. We conclude that (1) platelet particle formation can be induced by the generation of ROS; and (2) platelet PLA(2), 12-LO, NADPH oxidase, and cytosol membrane translocation, requirements for ROS production, are inhibited by Dex.

Calcimycin (A-23187) is an antibiotic and a unique divalent cation ionophore (like calcium and magnesium). Calcimycin induces Ca2+-dependent cell death by increasing intracellular calcium concentration. Calcimycin inhibits the growth of Gram-positive bacteria and some fungi. Calcimycin also inhibits the activity of ATPase and uncouples oxidative phosphorylation of mammalian cells. Calcimycin induces apoptosis.

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