Active membrane fluctuations studied by micropipet aspiration - art. no. 021908

We present a detailed analysis of the micropipet experiments recently repor ted by J-B. Manneville et al., [Phys. Rev. Lett. 82, 4356 (1999)], includin g a derivation of the expected behavior of the membrane tension as a functi on of the areal strain in the case of an active membrane, i.e., containing a nonequilibrium noise source. We give a general expression, which takes in to account the effect of active centers both directly on the membrane and o n the embedding fluid dynamics, keeping track of the coupling between the d ensity of active centers and the membrane curvature. The data of the microp ipet experiments are well reproduced by our expressions. In particular, we show that a natural choice of the parameters quantifying the strength of th e active noise explains both the large amplitude of the observed effects an d its remarkable insensitivity to the active-center density in the investig ated range.