Preface_1977_Dynamic-Aspects-of-Cell-Surface-Organization

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Preface 
There is now general acceptance of the view that the plasma membranes of 
most, if not all, cells are dynamic assemblies of molecules that are able to 
undergo rapid and reversible structural rearrangements in response to both 
intra- and extracellular stimuli. This concept is, however, of relatively recent 
origin. Until the mid-nineteen sixties, experimental observations on the mor­
phology, chemical composition and function of biological membranes were in­
terpreted against a conceptual background in which membrane components 
were thought to exist largely in rather rigid, ordered and static structural 
arrangements. In the late nineteen sixties and early seventies information 
began to accumulate from studies in a variety of disciplines which indicated 
that certain membrane components were free to move within the membrane 
and thus undergo topographic rearrangement. These findings were difficult to 
reconcile with the existing static models for membrane structure and prompted 
the formulation of new generalized concepts for membrane organization such 
as the "liquid crystalline,, and "fluid mosaic" models which, for the first time, 
appeared to fit the growing number of observations on the dynamic properties 
of biological membranes. From these initial experimental observations less than 
a decade ago, information on membrane dynamics has grown at a remarkable 
pace so that today the literature on the subject is of voluminous proportion. 
Although many fundamental questions remain to be answered, and speculation 
currently surrounds interpretation of several aspects of the subject, sufficient 
information is already available to support a functional relationship between 
the topography and dynamics of plasma membrane macromolecules and the 
control of cell surface properties. 
In its most simple form, the plasma membrane can be thought of as a 
two-dimensional solution of a mosaic of lipids and proteins. The lipids, ar­
ranged predominantly as a bilayer, exist in a "fluid'' state while the proteins 
(and glycoproteins) are either inserted to varying depths into the lipid bilayer 
(integral proteins) or bound loosely to the surfaces of the bilayer (peripheral 
proteins). Both proteins and lipids can be organized asymmetrically within this 
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type of structure, thus allowing specific classes of membrane components to be 
localized exclusively or predominantly at the inner or outer membrane surface. 
Another important feature is that the fluid state of the membrane lipids 
permits lateral diffusion of macromolecules within the plane of the membrane, 
thereby creating opportunities for rapid and reversible changes in membrane 
topography. The distinctive lateral mobilities of different membrane com­
ponents, ranging from extremely rapid to relatively immobile, permits cells to 
maintain certain surface molecules in relatively ordered topographic arrays or 
"patterns", while allowing others to diffuse randomly and avoid ordered 
topographic restraint. The fluid nature of cell membranes also dictates that 
environmental changes in temperature, ionic strength, pressure, binding of 
material to membrane "receptors" and many other stimuli can induce drastic 
changes in the physical state of the membrane, leading to phase changes and 
separations whereby molecules are excluded away from or sequestered into 
specific membrane regions or domains. Finally, trans-membrane interaction of 
components within the plasma membrane with membrane-associated structures 
in the cytoplasm offers a potential mechanism for the transmission of "in­
formation" across the membrane in either direction via various combinations 
of cooperative, allosteric and transductive coupling mechanisms. These and 
other possible regulatory devices may well allow different cell types to react 
individually to the same stimuli, thereby creating opportunities for a large 
repertoire of cell-specific responses and membrane specialization based on a 
relatively restricted and conservative framework of membrane structure. 
Membrane dynamics embraces a broad range of physical, chemical and 
biological processes. Comprehensive discussion of this subject demands con­
sideration of the basic physico-chemical properties of the different molecules 
and macromolecules found in membranes, analysis of their functional in­
terrelationships within membranes, characterization of the diverse factors that 
influence membrane organization in both physiological and pathological states 
and, finally, identification of relationships between the control of plasma 
membrane organization and changes in cell surface properties and cell be­
havior. Insight into these various aspects of membrane dynamics has come 
from work in many disciplines, from detailed observations at the molecular 
level as well as phenomenological descriptions of the behavior of intact cells, 
and from the application of numerous techniques, some old but improved, and 
some entirely new. 
This volume, the third in the Cell Surface Reviews series, contains fourteen 
chapters which reflect the dramatic growth of information of the dynamic 
nature of membrane organization. No attempt has been made to cover all 
aspects of this vast subject. However, the reviews in this volume offer a broad 
perspective of current concepts of plasma membrane organization and the 
range of experimental strategies and techniques used to investigate this im­
portant structure. Discussion of the importance of the biosynthesis, assembly 
and turnover of plasma membrane components in cell surface dynamics has 
been largely excluded from this volume since the next volume in this series will 
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be devoted entirely to this subject. Together, volumes 3 and 4 of Cell Surface 
Reviews provide an extensive and up-to-date discussion of what we feel to be 
the more important aspects of cell surface dynamics. 
We thank the contributors for their authoritative and comprehensive chap­
ters. We are also grateful to Judy Kaiser, Adele Brodginski, Shirley Guagliardi 
and Molly Terhaar for their assistance in preparing the edited manuscripts. 
George Poste 
Buffalo, New York 
August, 1976 
Garth L. Nicolson 
Irvine, California 
August, 1976