Valinomycin induced energy-dependent mitochondrial swelling, cytochrome c release, cytosolic NADH/cytochrome c oxidation and apoptosis

Abstract

In valinomycin induced stimulation of mitochondrial energy dependent reversible swelling, supported by succinate oxidation, cytochrome c (cyto-c) and sulfite oxidase (Sox) [both present in the mitochondrial intermembrane space (MIS)] are released outside. This effect can be observed at a valinomycin concentration as low as 1 nM. The rate of cytosolic NADH/cyto-c electron transport pathway is also greatly stimulated. The test on the permeability of mitochondrial outer membrane to exogenous cyto-c rules out the possibility that the increased rate of exogenous NADH oxidation could be ascribed either to extensively damaged or broken mitochondria. Accumulation of potassium inside the mitochondria, mediated by the highly specific ionophore valinomycin, promotes an increase in the volume of matrix (evidenced by swelling) and the interaction points between the two mitochondrial membranes are expected to increase. The data reported and those previously published are consistent with the view that "respiratory contact sites" are involved in the transfer of reducing equivalents from cytosol to inside the mitochondria both in the absence and the presence of valinomycin. Magnesium ions prevent at least in part the valinomycin effects. Rather than to the dissipation of membrane potential, the pro-apoptotic property of valinomycin can be ascribed to both the release of cyto-c from mitochondria to cytosol and the increased rate of cytosolic NADH coupled with an increased availability of energy in the form of glycolytic ATP, useful for the correct execution of apoptotic program.

Perturbation of intracellular K+ homeostasis with valinomycin promotes cell death by mitochondrial swelling and autophagic processes

“…There are also reports of valinomycin-induced swelling of mitochondria, which is more characteristic for a necrotic cell death mode than for apoptosis [23,43]. It has also been shown, that valinomycin induces swelling of isolated mitochondria, which leads to a release of cytochrome c [44]. Similarly, we observed swollen and structurally deformed mitochondria in valinomycin-exposed cells.…”

Site‐dependent biological activity of valinomycin analogs bearing derivatizable hydroxyl sites

“…Other relevant hints supporting the aforementioned facts came from the evaluation of the efficiency of each HyVLM in accelerating mitochondrial respiration and volume change (swelling), in comparison with VLM . It is well established that to compensate for the VLM‐induced dissipation of ΔΨ m (setup by respiration), mitochondria respond by speeding up their respiratory rate and oxygen uptake, in a dose‐dependent manner , so that the faster the respiration, the more efficient is the depolarizing agent under similar conditions.…”

Early-Stage Development of Novel Cyclodextrin-siRNA Nanocomplexes Allows for Successful Postnebulization Transfection of Bronchial Epithelial Cells

“…Valinomycin is a K + ionophore that selectively transports K + ions through the cell membrane leading to mitochondrial swelling, cytochrome c release, and autophagic processes. (28,29) In contrast, MG132 is a peptide aldehyde and is a potent inhibitor of the 26S proteasome complex that effectively blocks its proteolytic activity via the chymotrypsin degradation pathway. (30) Doses as low as 1-30 lM (compared with 120 lM for valinomycin) have been found to result in S-phase arrest in the cell cycle (31) and as such is a potent mediator of apoptosis.…”