Actions of ionomycin, 4-BrA23187 and a novel electrogenic Ca2+ ionophore on mitochondria in intact cells.

TitleActions of ionomycin, 4-BrA23187 and a novel electrogenic Ca2+ ionophore on mitochondria in intact cells.
Publication TypeJournal Article
Year of Publication2003
AuthorsAbramov, AY, Duchen, MR
JournalCell Calcium
Date Published2003 Feb
KeywordsAnimals, Benzoates, Bridged Bicyclo Compounds, Calcimycin, Calcium, Calcium Signaling, Cell Membrane Permeability, Coculture Techniques, Cycloheptanes, Cyclosporine, Cytosol, Endoplasmic Reticulum, Enzyme Inhibitors, Eukaryotic Cells, Humans, Intracellular Membranes, Ionomycin, Ionophores, Membrane Potentials, Mitochondria, Neurons, Rats, Sesquiterpenes, Sodium-Calcium Exchanger, Tumor Cells, Cultured

We have used fluorescence digital imaging techniques to explore the actions of two groups of Ca(2+) ionophores: (i). ferutinin, an electrogenic naturally occurring ionophore, and (ii). the neutral ionophores 4-BrA23187 and ionomycin, on cytosolic [Ca(2+)] ([Ca(2+)](c)), mitochondrial [Ca(2+)] ([Ca(2+)](m)) and mitochondrial membrane potential (deltapsi(m)) in HepG2 cells and primary hippocampal neurones in culture. 4-BrA23187 and ionomycin promoted the equilibration of [Ca(2+)] gradients between cellular compartments, including ER, mitochondria and cytosol. Thus, [Ca(2+)](c) and [Ca(2+)](m) increased together and then recovered in parallel on removal of the ionophore. In contrast, following a rise in [Ca(2+)](c) in response to ferutinin, [Ca(2+)](m) remained elevated for prolonged periods after the recovery of [Ca(2+)](c) levels despite washout of the compound. Both groups of Ca(2+) ionophores caused some mitochondrial depolarisation, although this was highly variable in degree. Mitochondrial depolarisation induced by ionomycin and 4-BrA23187 was often modest, independent of cyclosporin A (CsA), was suppressed in the absence of extracellular Ca(2+) and was enhanced by pre-incubation of cells with the inhibitor of the mitochondrial Ca(2+)/2Na(+)-exchanger, CGP37157, suggesting that the change in potential reflects the prior state of mitochondrial calcium loading. The mitochondrial depolarisation induced by ferutinin was not influenced by CGP37157 but was completely blocked by CsA, suggesting that it reflects opening of the mitochondrial permeability transition pore (mPTP). We suggest that ferutinin may provide a very valuable tool to promote mitochondrial calcium overload experimentally and to promote calcium-dependent opening of the mPTP.

Alternate JournalCell Calcium
Citation Key10.1016/S0143-4160(02)00203-8
PubMed ID12531186