Surface of cells

Section 25 16 Carbohydrates and proteins that are connected by a chemical bond are called glycoproteins and often occur on the surfaces of cells They play an impor tant role m the recognition events connected with the immune response... 

The epidermal growth factor receptor 2 (HER-2) is a protein found on the surface of cells. Heterodimerization of HER-2 activates the enzyme tyrosine kinase, triggering reactions that cause the cells to grow and multiply. HER-2 is found at abnormally high levels on the surface of many types of cancer cells, which may divide excessively. Antibodies targeting HER-2 (e.g., trastuzumab) are used as antineoplastic agents. 

One of the early events of the apoptotic process involves the translocation of phosphatidylserine on the surface of cell membranes annexin V binding and propidium iodide uptake reveals various cellular states. After treatment with organotin(IV) compounds the cells could be categorized into populations vital cells (annexin V /P ), early apoptotic cells (annexin V /P ), late apoptotic cells (annexin V /P ), and necrotic cells (annexin V /P" ). Cells are observed with a fluorescence microscope and it is possible to observe translocation of phosphatidylserine (PS) from the inner side of the plasma membrane to the outer one and to see a green stain for annexin V FLUOS bound to PS, and a red stain for propidium iodide. 

Cyclic AMP (cAMP) (Figure 18-5) is formed from ATP by adenylyl cyclase at the inner surface of cell membranes and acts as an intracellular second messenger in response to hormones such as epinephrine, norepinephrine, and glucagon. cAMP is hydrolyzed by phosphodiesterase, so terminating hormone action. In hver, insulin increases the activity of phosphodiesterase. 

P-glycoprotein is not only expressed in tumor cells, but also in cells of several healthy tissues. In liver it was detected in the biliary canalicular surface of hepato-cytes and the apical surface of small biliary ductules. In the small intestine and colon, it is localized in the apical surface of columnar epithelial cells, and in kidneys it is found in the brush border membrane of proximal tubules. Moreover, it is detectable on the apical surface of small ductules in the pancreas and on the surface of cells in the medulla and cortex of adrenals [2]. 

TEG macrostructure differs from that of natural graphite it possesses abnormally high porosity and highly developed active surface (40-50 m2/g) (Figure 1). The performed thermochemical treatment leads to an essential exfoliation of graphite matrix with a formation of cellular structure. The thickness of cell s walls is equal to 20-25 nm. The surface of cell s walls contains a lot of macrocracks, outcrops of crystallites, etc. The thermochemical re-treatment was applied to enhance TEG dispersivity. 

It is important that the method used to detach cells from their growing surface is compatible with end use. For final use as cell control material, it is important to use a methodology that preserves structural integrity and membrane protein localization. Enzymatic-based reagents may affect proteins on the surface of cells. 

Taking into account that ROS produced by irradiated fullerenes C60 may act only in the radius of their short diffusion existence, one may suppose that cytotoxic effect is determined by the interaction of fullerene C60 with the surface of cells and initiation of chain reactions of free radical peroxidation in membranes. That is why the influence of photoexcited fullerene C60 on the course of LPO process was studied and evaluated by the content of generated primary (diene conjugates) and final (Schiff bases) products. The content of diene conjugates in thymocytes was 17.7 4.2, inEAC cells was 21.1 1.3, andinL1210 was 12.8 3.1 nM/mg protein, and Schiff bases -56 7.9,46.5 4.5, and 36.6 4.6 rel. units/mg protein, respectively, and did not alter during 1 h incubation of the cells. 

Some reports showed that pure CNTs can cross cell membrane with high efficiency (Kam et al., 2005 Pantarotto et al., 2004). Some reports showed that CNTs could not be found in cells by HR-TEM (Carrero-Sanchez et al., 2006 Stone and Donaldson, 2006). In our previous studies, we also found that pure CNTs were very difficult to enter into cells such as human fibroblast cells (Tian et al., 2006) and HEK293 cells (Cui et al., 2005), and stem cells, we spent almost 6 months on sectioning these cells and looking for CNTs within cells by HR-TEM, finally we could not find CNTs within cells, we only observed that a lot of CNTs attached to the surface of cells (Fig. 9.10a), and some tubers appeared on the surface of CNTs (Fig. 9.10c). That is to say, non-modified CNTs enter into cells via low-efficient means. However, biomolecules-modified CNTs can efficiently enter into almost all... 

Fig. 9.10 SWCNTs attached to the surface of cells and located within cells a. SWCNTs attached to the surface of cells b. SWCNTs labeled with Cy3 located within cells c. Some protuberances appeared on the cell surface after cells are stimulated by SWCNTs. Right picture is control. Bar is 10 pm (With permission from American Scientific publisher) (See Color Plates)...

Another TIR/FRAP study on biological cell membranes has examined the reversible but specific binding kinetics of fluorescence-labeled epidermal growth factor to the surface of cells.(125) The background problem here was solved simply by choosing cells with a very large concentration of epidermal... 

Methods used to demonstrate the existence of membrane phospholipid asymmetry, such as chemical labelling and susceptibility to hydrolysis or modification by phospholipases and other enzymes, are rmsuitable for dynamic studies because the rates of chemical and biochemical reactions are of a different order compared to the transmembrane translocahon of the phospholipids. Indirect methods have therefore been developed to measure the translocation rate which are consequent on the loss of membrane phospholipid asymmetry. Thus time scales appropriate to rates of lipid scrambling under resting conditions or when the forces preserving the asymmetric phospholipid distribution are disturbed can be monitored. Generally the methods rely on detecting the appearance of phosphatidylserine on the surface of cells. Methods of demonstrating Upid translocation in mammalian cells has been the subject of a recent review (Bevers etal., 1999). 

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