Dicyclohexylcarbodiimide as inducer of mitochondrial Ca2+ release

Effect of hematoporphyrin monomethyl ether-mediated PDT on the mitochondria of canine breast cancer cells

Hematoporphyrin monomethyl ether (HMME) is a promising porphyrin-related photosensitize for photodynamic therapy (PDT). There still remains unknown changes regarding the mitochondrial in canine breast cancer cells treated with HMME-PDT. The aim of this study is to investigate the effect of HMME-PDT on structure and dysfunction of mitochondrial in cancer cells. The experimental approach included an initial study on the uptake of HMME using microscopic observation of the HMME-treated cells, optimization of the PDT-induced cell death by the MTT assay. These cells were then treated with HMME and a He-Ne laser at the wavelength of 632.8 nm following our optimized condition. Examination of mitochondrial changes by observing the stained cells under light microscope, mitochjondrial membrane potential flow cytometry, measuring the Ca(2+), SOD/GSH activity, ATPase and MDA contents for the mitochondria functions. The kinetics of HMME uptake in CHMm cells was determined and its cytocolic instead of nuclear distribution was demonstrated. The dose of 16mM HMME-PDT combined with 2.8 J/cm(2) laser irradiation was had the maximal impact on cell viability. This treatment resulted in structural changes in mitochondria that were accompanied with the loss of mitochjondrial membrane potential. As a result, HMME-PDT increased mitochondrial ROS, inhibited the enzymatic activities of mitochondrial SOD and GSH-Px, abolished mitochondrial ability in the uptake and release of calcium, and decreased mitochondrial ATPase activity. The combination of these abnormalities led to accumulation of ROS in mitochondrial to high levels, which in turn contributed to HMME-PDT-induced damages of mitochondrial structure and mitochondrial dysfunction.

Two critical factors affecting the release of mitochondrial cytochrome C as revealed by studies using N,N'-dicyclohexylcarbodiimide as an atypical inducer of permeability transition

N,N'-dicyclohexylcarbodiimide (DCCD) was earlier reported to have stimulatory effects on mitochondrial respiration and to induce mitochondrial swelling, when it was added to mitochondrial suspensions. These data seem to imply that DCCD caused the mitochondrial permeability transition (PT), but this possibility had never been investigated. In the present study, effects of DCCD on the mitochondrial structure and function were studied in detail. DCCD was found to induce mitochondrial PT in a cyclosporine A-insensitive manner. Electron microscopic analysis also supported the induction of the mitochondrial PT by DCCD. However, different from many other PT inducers, DCCD failed to cause massive release of mitochondrial cytochrome c. To understand the relationship between the induction of mitochondrial PT and the release of mitochondrial cytochrome c, we compared the actions of DCCD on mitochondrial structure and function with those of Ca2+, known as an ordinary PT inducer. As a result, two parameters considered to be critical for controlling the release of mitochondrial cytochrome c on the induction of PT were mitochondrial volume and the velocity of mitochondrial oxygen consumption.

Properties of a cyclosporin-insensitive permeability transition pore in yeast mitochondria

Yeast mitochondria (Saccharomyces cerevisiae) contain a permeability transition pore which is regulated differently than the pore in mammalian mitochondria. In a mannitol medium containing 10 mM Pi and ethanol (oxidizable substrate), yeast mitochondria accumulate large amounts of Ca2+ (>400 nmol/mg of protein) upon the addition of an electrophoretic Ca2+ ionophore (ETH129). Pore opening does not occur following Ca2+ uptake, even though ruthenium red-inhibited rat liver mitochondria undergo rapid pore opening under analogous conditions. However, a pore does arise in yeast mitochondria when Ca2+ and Pi are not present, as monitored by swelling, ultrastructure, and matrix solute release. Pore opening is slow unless a respiratory substrate is provided (ethanol or NADH) but also occurs rapidly in response to ATP (2 mM) when oligomycin is present. Pi and ADP inhibit pore opening (EC50 approximately 1 and 4 mM, respectively), however, cyclosporin A (7 microg/ml), oligomycin (20 microg/ml), or carboxyatractyloside (25 microM) have no effect. The pore arising during respiration is also inhibited by nigericin or uncoupler, indicating that an acidic matrix pH antagonizes the process. Pi also inhibits pore opening by lowering the matrix pH (Pi/OH- antiport). However, inhibition of the ATP-induced pore by Pi is seen in the presence of mersalyl, suggesting a second mechanism of action. Since pore induction by ATP is not sensitive to carboxyatractyloside, ATP appears to act at an external site and Pi may antagonize the interaction. Isoosmotic polyethylene glycol-induced contraction of yeast mitochondria swollen during respiration, or in the presence of ATP, is 50% effective at a solute size of 1.0-1.1 kDa. This suggests that the same pore is induced in both cases and is comparable in size with the permeability transition pore of heart and liver mitochondria.

Fluorescamine-induced membrane permeability in mitochondria

1. Addition of fluorescamine (75 microM) to mitochondria induced an increase in membrane permeability. 2. The leakiness of the inner mitochondrial membrane is characterized by extensive release of accumulated Ca2+, collapse of the transmembrane potential, mitochondrial swelling and efflux of matrix proteins, among them, malate dehydrogenase. 3. These effects were diminished by supplementing the media with 1 mM phosphate, and partially prevented by Mg2+. 4. These results indicate that the primary amino groups of membrane components contribute, partially, to the maintenance of the permeability barrier in mitochondria.