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Cells, Gels and Water: A Fresh Approach to Cell Function
Gerald Pollack, Professor of Bioengineering - University of Washington
March 2, 2007
Abstract
The cytoplasm is broadly acknowledged to be a polymer gel. Yet, textbook mechanisms build on the presumption that it is an aqueous solution. The concept of a gel-like cytoplasm is replete with power. Partitioning of ions between the inside and outside of the cell is directly explainable from the cytoplasm's gel-like character and the organization of its water molecules; such partitioning requires zero maintenance energy, unlike ion-pumping mechanisms. The cell's electrical potential is also explainable: substantial potentials are measured in gels, as well as in cells stripped of their membrane. Gels also undergo phase-transition - discontinuous transformation of protein and water from one physical state to another. In undergoing phase transition, the gels change volume, ion content, solvency, permeability, etc. - changes similar to those experienced by organelles within the functioning cell. The polymer-gel phase transition therefore has the potential to be a central paradigm for mediating many aspects of cell function. These ideas are explored in depth in a recent book (Pollack, "Cells, Gels and the Engines of Life," 2001, www.ebnerandsons.com), and will be discussed in the lecture. In considering these gel-based ideas, the state of water turns out to be of unexpectedly central significance. The cell is extremely crowded with surfaces; hence almost all water is interfacial. That interfacial water may differ from bulk water has been known for decades, but the extent of the interfacial zone has remained unclear. In a series of experiments undertaken to explore this issue (Zheng et al., Adv. Colloid Interface Sci. 127: 19-27, 2006), we find that surfaces impact water out to distances up to hundreds of micrometers. Evidence for this unexpectedly long-range impact will be presented.
Biography
Gerald Pollack received his Ph.D. in biomedical engineering from the Univ. of PA. His interests have ranged broadly in the areas of muscle contraction mechanisms and cell biology, with emphasis on nanoscale experimental approaches, and more recently also on the interaction of biological surfaces with aqueous solutions. In the muscle field, he pioneered many technological advances, the most recent of which is the nanolever (Fauver et al., 1998), which has been used to make nanoscale measurements on protein filaments, including the first dynamic measurements of single isolated muscle filaments sliding past one another (Liu and Pollack, 2004). In the interfacial water field, he co-organized and co-founded a Gordon Research Conference last year on "Interfacial Water in Cell Biology." His group (Zheng and Pollack, 2003) recently discovered a startling and unexpected phenomenon: solutes are excluded from a region hundreds of micrometers from various hydrophilic surfaces - a finding with broad implication for solute-surface interaction. Pollack's book, "Muscles and Molecules: Uncovering the Principles of Biological Motion" won an "Excellence Award" from the Society for Technical Communication. His latest book, "Cells, Gels and the Engines of Life" won that society's "Distinguished Award" and "Best in Show." Pollack was awarded an honorary Ph.D. from Ural State University and with the title Honorary Professor, Russian Academy of Sciences (Puschino). He has been awarded the Biomedical Engineering Society's Distinguished Lecturer Award, their highest honor. In 2003 he was IBC "International Scientist of the Year." Pollack is a Fellow of the American Heart Association, as well as a Founding Fellow of the American Institute of Medical and Biological Engineering (AIMBE).