In the past it was possible for theoreticians only to analyze the thermodynamic forces behind membrane shape-shifting. But now a team of biophysicists from Cornell University, the National Institutes of Health and the W.M. Keck Foundation has been able to watch the sacs, or vesicles, reshaping themselves under the light of multiphoton three-dimensional microscopy. The forces behind the membrane morphing, the researchers say, is akin to a party entertainer shaping balloon animals by tensioning the surfaces.
Their report on observing the membranes -- a laboratory-grown mixture of phospholipids and cholesterol -- being reshaped into two separate, two-dimensional liquid phases, or "rafts," appears in the latest issue of the journal Nature (Oct. 23, 2003; vol. 425, pp. 821-824) and is illustrated on the magazine's cover. The findings, say the researchers, should help cell biologists understand the functions of cell membranes that are important to human health.
"This is the first experiment to show interphase energetics influencing membrane geometries," says Cornell professor of applied physics Watt W. Webb, leader of the team. Tobias Baumgart, Cornell postdoctoral researcher, developed and analyzed the new experiments, and Samuel T. Hess of the National Institute of Child Health and Human Development, computed the theoretical shape "fits."
The interactions observed between separate phases of shape-shifting fluid membranes generally confirmed predictions made by German theoretician Reinhard Lipowsky and his colleagues. The observations also enabled measurement of the energetic tensions of the interphase lines separating the membrane rafts. In the immune system, defending macrophages engulf microbes and enclose the invaders in vesicles.
Contact: Roger Segelken
Cornell University News Service