| Regional Biophysics Meeting 2005, March 16-20, Zreče, Slovenia | [CellBiophys] |
Normal cells maintain a defined membrane fluidity which supports proper cell function. The membrane fluidity of proliferative tumor cells is affected by the cell density, the cell cycle and by the external conditions. The general trend in certain cell type is that the proliferative activity increases with membrane fluidity. The actual correspondence between membrane fluidity and unrestrained proliferation of tumor cells (tumourgeneicity) is not clear. On the dynamic level the lipid fluidity operates as a fractional force which oposes lateral and rotational mobility of membrane proteins and thus determines their rate of collisonal coupling to form active units, aggregates of receptors. Membrane lipid fluidity was measured as a relative proportion of the least ordered mode of spin label (5-doxyl derivative of palmitic acid methyl ester) motion using electron paramagnetic resonance (EPR). MLF depended on the cell density and the frequency of replacing cell medium. In addition to membrane fluildity changes also the lateral membrane domain structure changed in respect to cell density. In the exponential growing phase spin label experinenced five different modes of motion, while in the plato phase, at confluency, spin label reported only three modes of motion. This suggests that lipid membrane of cells has less lateral lipid domains at confluent conditions than lipid membrane of cells in the exponential growing phase. A biologocal membrane is a heterogeneous system consisting of a mosaic of co-existing phase domains. Membrane components are physically separated based on their solubility. It was already proposed that membrane percolating properties may serve as a potential trigger mechanism in the control of membrane physiology. We propose a membrane switch hypothesis: membrane lateral domain organization 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