Berlin 2012 – scientific programme

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BP: Fachverband Biologische Physik

BP 32: Physics of Cells III

BP 32.5: Talk

Friday, March 30, 2012, 10:30–10:45, H 1028

Active fluctuations of the red blood cell membrane violate the fluctuation dissipation theorem — •Timo Betz, Hervé Turlier, Jean-François Joanny, and Cécile Sykes — Institut Curie, UMR 168, 11 rue Pierre et Marie Curie, 75005 Paris, France

Red blood cells are extremely elastic objects, able to recover their shape even after large deformation as when passing through tight capillaries. Despite many decades of intensive research, the influence of active mechanical of red blood cells is still under debate. Here we present direct evidence that the red blood cell fluctuations violate the fluctuation dissipation theorem (FTD). We directly measure the mechanical response function using optical tweezers, and compare it to the thermal fluctuation spectrum represented by the power spectral density (PSD). In equilibrium thermodynamics, the dissipative part of the response function and the PSD are related by the fundamental relation of the fluctuation-dissipation theorem, which we directly tested with our measurements. The experimental investigation of the FDT shows a violation at the low frequency range (f<10Hz), while at higher frequencies the FDT is confirmed. This has important implications for the analysis of red blood cell mechanics, as the FDT is commonly used to extract mechanical parameters from membrane fluctuations. Using classical equilibrium membrane theory, we can show that the effect of the active fluctuations is manifested in an apparent lower membrane tension as compared to the direct measurement using the response function. Our results suggest that the active fluctuations help the RBC to pass through capillaries and to prevent adhesion.