Lipid membranes bilayer response

Phosphatidylcholine is an important component of cell membranes but cell mem branes are more than simply lipid bilayers Although their composition varies with their source a typical membrane contains about equal amounts of lipid and protein and the amount of cholesterol m the lipid fraction can approximate that of phosphatidylcholine The lipid fraction is responsible for the structure of the membrane Phosphatidyl choline provides the bilayer that is the barrier between what is inside the cell and what IS outside Cholesterol intermingles with the phosphatidylcholine to confer an extra measure of rigidity to the membrane... 

The lipid fraction is responsible for the structure of the membrane. Phosphatidylcholine provides the bilayer that is the banier between what is inside the cell and what is outside. Cholesterol intermingles with the phosphatidylcholine to confer an extra measure of r-igidity to the membrane. 

The cq receptors are activated not only by catecholamines but also by the hormones vasopressin and angiotensin n. Binding of these hormones to a, receptors induces a complex response that involves rapid hydrolysis of phosphatidylinositol derivatives and release of Ca2+ into die cytoplasm, and of diacylglycerols into the lipid bilayer of the membrane. The response is mediated by another G protein called Gq.27 1 275 When this G protein is activated it induces the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdInsP2), a normal minor component of the lipid bilayer, by phospholipase C (phosphoinositidase C).265,276 281... 

Use of bilayer lipid membranes as a generic electrochemical transducer is an exciting future for food biosensors. A taste sensor with multichanneled lipid membrane electrode was recently developed (93). The electric patterns generated from the sensor are similar to human response. The sensor can distinguish different brands of beer. More details on the taste sensor can be found in Chapter 16 of this book. 

The frequency response of various chemical constituents of nerve membrane was studied. Biological membranes in general consist of lipids and proteins. Firstly, impedance characteristics of artificial lipid bilayer membranes are examined using lecithin-hexadecane preparations. It was observed that the capacitance of plain lipid membranes was independent of frequency between 100 Hz and 20 KHz. Moreover, application of external voltages has no effect up to 200 mV. Secondly, membrane capacitance and conductance of nerve axon were investigated. There are three components in nerve membranes, i.e., conductance, capaci-... 

Acetylcholineesterase Bilayer lipid membranes were prepared by adding a solution of egg phosphatidylcholine and dipalmi-toyl phosphatidic acid dropwise into the surface of aqueous 0.1 M KC1/10 mM HEPES, near the Saran Wrap partition of a two compartment plexiglass cell. A portion of AChE solution in 10 mM Tris hydrochloride buffer solution of pH 7.4 was applied. The electrolyte level was momentarily dropped below the orifice and raised to form a membrane. The membranes were used as transducers for the reaction of AChE with ACh. An external voltage (25 mV) was applied across the membrane between two Ag/AgCl reference electrodes. Enzymatically generated hydronium ion causes transient current due to alteration of the electrostatic field by the ionization of dipalmitoyl phosphatidic acid. The response delay time was directly related to the substrate concentration where acetylcholine can be determined from 1 pM upto mM level. [113]... 

Due to their simplicity of construction, ease of modification, electrical methods of detection, fast response time and the fact that they are the principal structural component of all biomembranes, conventional bilayer lipid membrane (BLM) arises as an ideal system for biosensor technology [88] and they have been studied regarding the possibility of developing DNA biosensors consisting of a glassy carbon electrode-modified by a BLM with incorporated ssDNA [89]. 

In addition to receptor-type proteins, bilayer lipid membranes (BLMs) have been investigated for the detection of species of biochemical interest [221, 231,232]. The lipid film can be used alone, or chemical receptor agents can be incorporated into the membrane to enhance selectivity for inorganic ions or organic compounds/ions. Responses for BLM-coated devices are related to the mass loading of the analyte in/on the lipid film and to changes in interfacial conditions, e.g., elastic and viscous coupling effects [53,221-223]. 

At frequencies below 63 Hz, the double-layer capacitance began to dominate the overall impedance of the membrane electrode. The electric potential profile of a bilayer membrane consists of a hydrocarbon core layer and an electrical double layer (49). The dipolar potential, which originates from the lipid bilayer head-group zone and the incorporated protein, partially controls transmembrane ion transport. The model equivalent circuit presented here accounts for the response as a function of frequency of both the hydrocarbon core layer and the double layer at the membrane-water interface. The value of Cdl from the best curve fit for the membrane-coated electrode is lower than that for the bare PtO interface. For the membrane-coated electrode, the model gives a polarization resistance, of 80 kfl compared with 5 kfl for the bare PtO electrode. Formation of the lipid membrane creates a dipolar potential at the interface that results in higher Rdl. The incorporated rhodopsin may also extend the double layer, which makes the layer more diffuse and, therefore, decreases C. ... 

Phase separation of non-bilayer forming lipids could be responsible for initiating the modification in the thylakoid membrane structure... 

CXCRl is a receptor for the chemokine interleukin-8 (IL-8), a mediator of immune and inflammatory responses. Strategically located in the cell membrane, CXCRl binds to IL-8 with high affinity and subsequently transduces a signal across the membrane bilayer to a G-protein-activated second messenger system. Reserchers describe NMR studies of the interactions between IL-8 and human CXCRl in lipid enviromnents. A combination of solution NMR and solid-state NMR studies of IL-8 in the presence of various constructs of CXCRl enables us to propose a model for the multi-step binding process. ... 

Researchers have studied whether acyl-chain order could be responsible for the preferred sterol interaction with SMs. Acyl-chain order was deduced from diphenylhexatriene anisotropy and from the deuterium order parameter obtained by H-NMR on bilayers made from either 14 0/14 0(d27)-PC, or 14 0(d27)-SM7 Some researcher analyzed the ground and excited states of phospholamban (PLN), a membrane protein that regulates sarcoplasmic reticulum (SR) calcium ATPase (SERCA), in dilferent membrane mimetic environments. Gustavsson et al. have previously proposed that the conformational equilibrium of PLN are central to SERCA regulation. They have now shown that these equilibrium detected in micelles and bicelles are also present in native sarcoplasmic reticulum lipid membranes as probed by MAS solid-state NMR. ... 

---