Membrane dynamics, living systems

The liquid crystalline phase is most relevant to membranes in living systems and represents a good description for the cell membrane, even though real membrane nanoscale structure may be highly complex and dynamic. In the following section, we explore some of the interesting membrane phase behavior that has been seen in mixed-lipid membranes and its relevance to real biological systems. 

Fluorescence is also a powerful tool for investigating the structure and dynamics of matter or living systems at a molecular or supramolecular level. Polymers, solutions of surfactants, solid surfaces, biological membranes, proteins, nucleic acids and living cells are well-known examples of systems in which estimates of local parameters such as polarity, fluidity, order, molecular mobility and electrical potential is possible by means of fluorescent molecules playing the role of probes. The latter can be intrinsic or introduced on purpose. The high sensitivity of fluo-rimetric methods in conjunction with the specificity of the response of probes to their microenvironment contribute towards the success of this approach. Another factor is the ability of probes to provide information on dynamics of fast phenomena and/or the structural parameters of the system under study. 

Liquid crystals are widely believed to be closely related to membranes of living cells and have been used as model systems in studies to understand membrane behavior. Among dynamic processes of interest here are transport of various species across membranes and various motions and deformations of membranes. 

Finally, Section 2.4 analyses a simplified model of a bursting pancreatic /3-cell [12]. The purpose of this section is to underline the importance of complex nonlinear dynamic phenomena in biomedical systems. Living systems operate under far-from-equilibrium conditions. This implies that, contrary to the conventional assumption of homeostasis, many regulatory mechanisms are actually unstable and produce self-sustained oscillatory dynamics. The electrophysiological processes of the pancreatic /3-cell display (at least) two interacting oscillatory processes A fast process associated with the K+ dynamics and a much slower process associated with the Ca2+ dynamics. Together these two processes can explain the characteristic bursting dynamics in the membrane potential. 

Tsong, T. Y. Chauvin, F. Astumian, R. D. Interaction of membrane proteins with static and dynamic electric fields via electroconformational coupling. In Mechanistic Approaches to Interaction of Electromagnetic Fields with Living Systems Blank, M. Findl, E., Eds. Plenum New York pp 187-202. 

As is characteristic of most individual components of living systems, receptors are not static but, rather, are constantly in a state of dynamic adaptation. One could envision these protein molecules floating vi/ithin the fluid mosaic of the biological membrane awaiting interaction with normal physiological signals. The... 

CARS microscopy has emerged as a highly sensitive analytical tool for vibrational bioimaging, predominantly, of lipids in membrane model systems [69, 81-84], live unstained cells [85-95, 43], and both ex vivo and in vivo tissues [26, 96-103, 43]. Examples of CARS imaging applications in the physical and material sciences include the study of fracture dynamics in drying silica nanoparticle suspensions [104], patterned polymeric photoresist film [105], drug molecules in a polymer matrix [106], and liquid crystals [107, 108],... 

Biosensors based on metal-supported bilayer lipid membranes. BLMs, especially s-BLMs, have been used in the last three years as lipid bilayer-based biosensors [10,11,74-76,82], Hianik etal [75] have carried out a detailed physical study on the elasticity modulus of s-BLMs. They found that the dynamic viscosity of s-BLMs is one order of magnitude less than that of conventional BLMs [75]. It should be mentioned that in the s-BLM system, albeit attractive for certain purposes such as biosensors and molecular devices, the metallic substrate precludes ion translocation across the lipid bilayer. Therefore, the pursuit of a simple method for obtaining long-lived, planar BLMs separating two aqueous media has been an elusive one until now [81]. As reported, this much improved... 

Model systems range from the unique water structures at solid surfaces and water shells around proteins and biomembranes, via amino and nucleic acids, proteins, DNA, phospholipid membranes, to cells and living tissue at surfaces. At one end of the spectrum the scientific challenge is to map out the structures, bonding, dynamics and kinetics of biomolecules at surfaces in a similar way as has been done for simple molecules during the past three decades in surface science. At the other end of the complexity spectrum one addresses how biofunctional surfaces participate in and can be designed to constructively participate in the total communication system of cells and tissue. ... 

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