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.