Cell membranes membrane fluidity

Liposomes are considered as substantial models for the study of biological membranes. They have many physicochemical properties, such as membranes permeability, osmotic activity, interaction with various solutes, surface characteristics and chemical composition similar to cell membranes. The fluidity of their membranes and their self-closed structure are essential parameters for the study of the biological membrane function. 

The primary site of action is postulated to be the Hpid matrix of cell membranes. The Hpid properties which are said to be altered vary from theory to theory and include enhancing membrane fluidity volume expansion melting of gel phases increasing membrane thickness, surface tension, and lateral surface pressure and encouraging the formation of polar dislocations (10,11). Most theories postulate that changes in the Hpids influence the activities of cmcial membrane proteins such as ion channels. The Hpid theories suffer from an important drawback at clinically used concentrations, the effects of inhalational anesthetics on Hpid bilayers are very small and essentially undetectable (6,12,13). 

A molecular variation of plasma membrane has been reported by Puccia et al. Reduction of total lipids (XL) content and significant variations of triglyceride (TG) and phospholipids (PL) fractions were observed as a consequence of exposure of C. intestinalis ovaries to TBTCl solutions. In particular, an evident TG decrease and a PL increase were observed, which probably provoked an increment in membrane fluidity, because of the high concentration of long chain fatty acids and, as a consequence, PL. This could be a cell-adaptive standing mechanism toward the pollutants, as observed in Saccharomyces cerevisiae. Also the increase in the content of the polyunsaturated fatty acids (PUPA), important in the synthesis of compounds such as prostaglandin which are present in the ovary in a stress situation, was probably a consequence of a defense mechanism to the stress provoked by the presence of TBTCl. 

This proves our theory that the membrane fluidity is an important parameter increasing shear stress resistance. The studies give two possibilities of improving the resistance lowering temperature or adding cholesterol. Which one is the most convenient is dependent on the cell line and the constraints of the process. 

The use of Upid bilayers as a relevant model of biological membranes has provided important information on the structure and function of cell membranes. To utilize the function of cell membrane components for practical applications, a stabilization of Upid bilayers is imperative, because free-standing bilayer lipid membranes (BLMs) typically survive for minutes to hours and are very sensitive to vibration and mechanical shocks [156,157]. The following concept introduces S-layer proteins as supporting structures for BLMs (Fig. 15c) with largely retained physical features (e.g., thickness of the bilayer, fluidity). Electrophysical and spectroscopical studies have been performed to assess the appUcation potential of S-layer-supported lipid membranes. The S-layer protein used in aU studies on planar BLMs was isolated fromB. coagulans E38/vl. 

The red blood cell must be able to squeeze through some tight spots in the microcirculation during its numerous passages around the body the sinusoids of the spleen are of special importance in this regard. For the red cell to be easily and reversibly deformable, its membrane must be both fluid and flexible it should also preserve its biconcave shape, since this facilitates gas exchange. Membrane lipids help determine membrane fluidity. Attached to the inner aspect of the membrane of the red blood cell are a number of peripheral cytoskeletal proteins (Table 52-6) that play important roles in respect to preserving shape and flexibility these will now be described. 

The lipid molecule is the main constituent of biological cell membranes. In aqueous solutions amphiphilic lipid molecules form self-assembled structures such as bilayer vesicles, inverse hexagonal and multi-lamellar patterns, and so on. Among these lipid assemblies, construction of the lipid bilayer on a solid substrate has long attracted much attention due to the many possibilities it presents for scientific and practical applications [4]. Use of an artificial lipid bilayer often gives insight into important aspects ofbiological cell membranes [5-7]. The wealth of functionality of this artificial structure is the result of its own chemical and physical properties, for example, two-dimensional fluidity, bio-compatibility, elasticity, and rich chemical composition. 

Before the first indication of the existence of cannabinoid receptors, the prevailing theory on the mechanism of cannabinoid activity was that cannabinoids exert their effects by nonspecific interactions with cell membrane lipids (Makriyannis, 1990). Such interactions can increase the membrane fluidity, perturb the lipid bilayer and concomitantly alter the function of membrane-associated proteins (Loh, 1980). A plethora of experimental evidence suggests that cannabinoids interact with membrane lipids and modify the properties of membranes. However, the relevance of these phenomena to biological activities is still only, at best, correlative. An important conundrum associated with the membrane theories of cannabinoid activity is uncertainty over whether cannabinoids can achieve in vivo membrane concentrations comparable to the relatively high concentrations used in in vitro biophysical studies (Makriyannis, 1995). It may be possible that local high concentrations are attainable under certain physiological circumstances, and, if so, some of the cannabinoid activities may indeed be mediated through membrane perturbation. 

Unsaturations of lipids play a key role in lipid homeostasis, where organisms adapt to temperature variations of the environment. Plants and animals maintain physiological functions by reversibly altering the composition and conformation of lipid molecules of the cell membrane. To achieve this, they extensively and elegantly use the unsaturations (double bonds) present in their side chains. This is the process by which cell membranes adjust their flexibility (fluidity) of the bilayer and adapt themselves to perturbations in temperature, pressure, and other variations in the natural environment [11-14]. They remain indispensable for the poikilothermism exhibited by fishes, invertebrates, and amphibians [15, 16]. Commercially,... 

Haidekker MA, L Heureux N, Frangos JA (2000) Fluid shear stress increases membrane fluidity in endothelial cells a study with DCVJ fluorescence. Am J Physiol Heart Circ Physiol 278(4) H1401-H1406... 

Osterode W, Holler C, Ulberth F (1996) Nutritional antioxidants, red cell membrane fluidity and blood viscosity in type 1 (insulin dependent) diabetes mellitus. Diabet Med 13(12) 1044-1050... 

The transport behavior of Li+ across membranes has been the focus of numerous studies, the bulk of which have concentrated upon the human erythrocyte for which the Li+ transport pathways have been elucidated and are summarized below. The movement of Li+ across cell membranes is mediated by transport systems which normally transport other ions, therefore the normal intracellular and subcellular electrolyte balance is likely to be disturbed by this extra cation. Additionally, Li+ has been shown to increase membrane phospholipid unsaturation in rat brain, leading to enhanced fluidity in the membrane, which could have repercussions for membrane-associated proteins and for membrane transport properties. 

Solarization process increases soil temperatures up to levels lethal to many plant pathogens and pests and, therefore, direct thermal inactivation is the most important and normally expected mechanism. Some studies on the biochemical bases of sensitivity of organisms to high temperatures hypothesized that heat sensitivity is related to small differences in cell macromolecules, leading to a lethal increase of intra-molecular hydrogen, ionic, and disulfide bonds (Brock 1978). Sundarum (1986) suggested a reduced cell membrane function beyond an upper limit fluidity... 

Prostaglandins are a subgroup of a larger family of compounds known collectively as eicosanoids, which are synthesized from arachidonic acid (arachidonate) this is a 20-carbon omega-6 unsaturated fatty acid (C20 4). The source of the arachidonic acid for PG synthesis is the cell membrane. Most membrane phospholipids have an unsaturated fatty acid as arachidonate at carbon 2 on the glycerol backbone to help maintain membrane fluidity. The arachidonic acid released from the membrane by the... 

The rs is often equated with the term membrane fluidity, which itself is a vague term relating to the motional condition of membrane lipids. Nevertheless, membrane fluidity continues to be a useful concept in studies with natural cell membranes. This subject has been rigorously reviewed elsewhere 2 34) and will therefore not be dealt with in detail here. In spite of the problem that rs contains both rate and orientational contributions (see... 

J.-G. Kuhry, G. Kuportail, C. Bronner, and G. Laustriat, Plasma membrane fluidity measurements on whole living cells by fluorescence anisotropy of trimethylammonium-diphenylhexatriene, Biochim. Biophys. Acta 845, 60-67 (1985). 

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