Principle investigator: Fritz Scholz
Co-supervisor: U. Lendeckel

Recent experiments have proven that the adhesion-spreading of mitochondria [1], of thrombocyte vesicles [2], and of reconstituted plasma membrane vesicles of plant leaf and root cells on electrodes provide access to information on the fluidity of the membranes. The experiments follow the approach developed for liposomes [3,4,5]. These studies have shown that the flexibility of membranes, e.g., the flip-flop kinetics of lipid molecules, the activation energy of pore formation, the kinetics of spreading of the lipid molecules on the electrode surface, etc., can be monitored by chronoamperometric measurements of the adhesion-spreading events of liposomes on electrodes. The effect of NO on the adhesion-spreading kinetics of reconstituted plasma membrane vesicles of plant leaf and root membranes is very pronounced and allows deducing important information on the role of NO as a signal molecule and cytotoxic radical. The studies of mitochondria isolated from insulinoma cells (β-cells, BRIN-BD11) showed that under hyperglycemic conditions the membrane flexibility was seriously decreased whereas the phase transition temperature remained unaffected1. These results show that studies of the adhesion-spreading behaviour of mitochondria are potentially well suited to access the effects of ROS/RNS on the membranes of cell organelles. The present project has the aims to perform detailed studies on the effects of ROS/RNS on the membrane flexibility of human and plant mitochondria and to correlate the observed effects with pathophysiological observations. The signals of mitochondria arise from a disintegration of the outer and inner membrane. The exposure levels of mitochondria to ROS/RNS will be varied by deliberately changing the growth conditions and cardipolipin components of the cells (e.g., by variation of glucose and fatty acid concentrations in the diet of insulinoma cells). Parallel to the mitochondria studies, liposomes prepared from synthetic and natural cardiolipins will be investigated. The vesicles will be attacked by hydroxyl radicals generated by the catalytic decomposition of H₂O₂ on platinum, thus avoiding any other chemical or physical effects on the liposomes. With this technique it has already been shown that hydroxyl radicals abstract one alkyl chain from a synthetic cardiolipin and form a lysocardiolipin, which tremendously changes the fluidity of the liposome membrane (publication in preparation). The experiments with liposomes made from synthetic and natural cardiolipins are aimed at facilitating the interpretation of the mitochondrial experiments. In case of OH attack on the cardiolipin liposomes the products of interaction will be studied by mass spectrometry (Schild) and by nuclear magnetic resonance spectroscopy B4 (Lalk/Kahlert). AFM/STM studies of lipid monolayers on solid supports are scheduled to monitor the OH attack on a nanoscopic level.

Literature

1 Hermes, M., Scholz. F., Härdtner, C., Walther, R., Schild, L., Wolke, C., Lendeckel, U.: Angew. Chem. Int. Ed. (2011) 50, 6872.

2 Agmo Hernández, A., Niessen, J., Harnisch, F., Block, S., Greinacher, A., Kroemer, H.K., Helm, C.A., Scholz, F.: Bioelectrochem. (2008) 74, 210.

3 Hellberg, D., Scholz. F., Schubert. F., Lovrić. M., Omanović. D., Agmo Hernández. V., Thede, R.: J. Phys. Chem. B (2005) 109, 14715.

4 Agmo Hernández, V., Scholz, F.: Langmuir (2006) 22, 10723.

5 Agmo Hernández, V., Scholz, F.: Israel J. Chem. (2008) 48, 169.