Active membrane fluctuations studied by micropipet aspiration

We present a detailed analysis of the micropipet experiments recently reported by J-B. Manneville et al., Phys. Rev. Lett. 82, 4356 (1999), including a derivation of the expected behavior of the membrane tension as a function 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 into account the effect of active centers both directly on the membrane and on the embedding fluid dynamics, keeping track of the coupling between the density of active centers and the membrane curvature. The data of the micropipet experiments are well reproduced by our expressions. In particular, we show that a natural choice of the parameters quantifying the strength of the active noise explains both the large amplitude of the observed effects and its remarkable insensitivity to the active-center density in the investigated range.