| Regional Biophysics Meeting 2005, March 16-20, Zreče, Slovenia | [CellBiophys] |
It is well known that normal cells maintain a defined membrane fluidity which supports proper cell function, while the membrane fluidity of proliferative tumor cells is affected by the cell density, the cell cycle and the external conditions. The general trend in certain cell type is that the proliferative activity increases with membrane fluidity. Lipid fluidity acts as a fractional force which opposes lateral and rotational mobility of membrane proteins and thus determines their rate of collisional coupling to form active units, aggregates of receptors, which could influence the proliferative activity of cells. A biological membrane is a heterogeneous system consisting of a mosaic of co-existing phase domains. Phases differ both chemically and physically among each other depending on the chemical structure of membrane components. To get better insight into the domain structure of malignant cell membranes the human breast cancer cells were spin labeled and their membrane properties were measured by electron paramagnetic resonance (EPR) in combination with GHOST condensation routine. It was found that in the exponential growing phase fatty acid spin label (5-doxyl derivative of palmitic acid methyl ester) experienced five different modes of motion, while in the plateau phase, at confluency, spin label reported only three modes of motion. This suggests that lipid membrane of cells has less lateral lipid domain types at confluent conditions than in the exponential growing phase. It was already proposed that percolating properties of membrane domains may serve as a potential trigger mechanism in the control of membrane physiology. In accordance to our experimental data we propose a membrane switch hypothesis: disappearance of certain membrane domain types might act as a switch allowing clustering of receptors into active units in the same lipid membrane domain and thus influencing physiology of cells.
Email: tilen.koklic@ijs.si
Address: EPR Center, Jozef Stefan Institute, Jamova 39, 1001 Ljubljana, Slovenia