The physics of active membranes

We review recent work on the physical properties of model fluid membranes i n nonequilibrium situations resembling those encountered in the living cell and contrast their properties with those of the more familiar membranes at thermal equilibrium. We survey models for the effect of (i) active pumps a nd (ii) active fission-fusion processes encountered in intracellular traffi cking on the stability and fluctuations of fluid membranes. Our purpose is twofold: to highlight the exciting nonequilibrium phenomena that arise in b iological systems, and to show how some crucial features of living systems, namely dissipative energy uptake and directed motion, can fruitfully be in corporated into physical models of biological interest. (C) 2001 Academie d es sciences/Editions scientifiques et medicales Elsevier SAS.