ubiquinone and 5-5--6-6--tetrachloro-1-1--3-3--tetraethylbenzimidazolocarbocyanine

Coated-platelets are a subset of cells observed during costimulation of platelets with collagen and thrombin. Important characteristics of coated-platelets include retention of multiple alpha-granule proteins and expression of phosphatidylserine on the cell surface. The mitochondrial permeability transition pore (MPTP) is a key step in apoptosis and is suggested to be involved in some forms of platelet activation. The objective of this study was to examine the role of MPTP in the synthesis of coated-platelets.. Flow cytometric analysis of coated-platelet production was used to examine the impact of pharmacological effectors of MPTP formation. Cyclosporin A, coenzyme Q, and bongkrekic acid all inhibit MPTP formation as well as production of coated-platelets. Phenylarsine oxide and diamide, both potentiators of MPTP formation, stimulate coated-platelet synthesis. Atractyloside, another inducer of MPTP formation, does not affect the percentage of coated-platelets synthesized; however, it does increase the level of phosphatidylserine exposed on the surface of coated-platelets.. These findings indicate that MPTP formation is an integral event in the synthesis of coated-platelets. Although the exact function of the MPTP remains to be determined, these data support a growing body of evidence that apoptosis-associated events are vital components of the platelet activation process. Formation of coated-platelets involves a complex set of activation events initiated by dual agonist activation. The mitochondrial permeability transition pore (MPTP) is a key intermediate in apoptosis and has been suggested to impact platelet activation. This report demonstrates that MPTP formation is essential to production of coated-platelets.

Topics: Adult; Apoptosis; Arsenicals; Atractyloside; Benzimidazoles; Blood Platelets; Bongkrekic Acid; Carbocyanines; Collagen; Crotalid Venoms; Cyclosporine; Cytoplasmic Granules; Diamide; Drug Synergism; Flow Cytometry; Fluorescent Dyes; Humans; Ion Channels; Lectins, C-Type; Membrane Lipids; Mitochondrial Membrane Transport Proteins; Mitochondrial Permeability Transition Pore; Phosphatidylserines; Platelet Activation; Thrombin; Thromboplastin; Ubiquinone

Defects in mitochondrial energy metabolism due to respiratory chain disorders lead to a decrease in mitochondrial membrane potential (DeltaPsim) and induce apoptosis. Since coenzyme Q10 (CoQ10) plays a dual role as an antioxidant and bioenergetic agent in the respiratory chain, it has attracted increasing attention concerning the prevention of apoptosis in mitochondrial diseases. In this study the potential of CoQ10 to antagonize the apoptosis-inducing effects of the respiratory chain inhibitor rotenone was explored by video-enhanced microscopy in SH-SY5Y neuroblastoma cells. The cationic fluorescent dye JC-1 which exhibits potential-dependent accumulation in mitochondria was used as an indicator to monitor changes in DeltaPsim. The relative changes in fluorescence intensity after incubation with rotenone for 15 minutes were calculated. Pre-treatment with CoQ10 (10 or 100 microM) for 48 h led to a significant reduction of rotenone-induced loss of DeltaPsim. These results suggest, that cytoprotection by CoQ10 may be mediated by raising cellular resistance against the initiating steps of apoptosis, namely the decrease of DeltaPsim. Whether these data may provide new directions for the development of neuroprotective strategies has to be investigated in future studies.

Topics: Antioxidants; Apoptosis; Benzimidazoles; Carbocyanines; Coenzymes; Cytoprotection; Electron Transport; Electron Transport Complex I; Energy Metabolism; Enzyme Inhibitors; Fluorescent Dyes; Humans; Membrane Potentials; Mitochondria; Neuroblastoma; Neurons; Rotenone; Tumor Cells, Cultured; Ubiquinone