ATP-dependent mechanics of red blood cells
ATP-dependent mechanics of red blood cells, Timo Betz, Martin Lenz, Jean-Francois Joanny, and Cecile Sykes., PNAS vol.106 no.36 
The fluctuations of the membrane of red blood cells is studied using an optical deflection method similar to that used to detect the position of trapped colloids in an optical trap. Membrane fluctuations observed in the absence of ATP are regarded as occurring passively - that is they are thermal in nature. The frequency dependence of these thermal fluctiations is compared with membrane fluctuations occurring in the presence of APT, and a significant deviation from equilibrium statistics os observed.