Active adhesion interactions

Figure 7.1 Schematic of three types of cell—material surface interactions (a) nonadsorption interactions (h) passive adhesion interactions (c) active adhesion interactions.

The classical cadherins are translated as precursor because they are N-terminally cleaved to reveal the mature proteins. This processing is required to activate the cell adhesion function of cadherins. Cadherins interact in trans (i.e., from opposite cells) via the most N-terminal cadherin rqDeats. A short amino acid sequence within this repeat, histidine-alanine-valine (HAV), has been implicated in mediating cell-cell contacts as HAV peptides can disrupt cadherin-dependent cell adhesion. Besides the trans-interactions of cadherins, the extracellular domains are also capable of forming cis-dimers through lateral amino acid contacts between cadherin molecules on one cell. This dimerization again mainly involves the first cadherin repeat. A zipper model based on the pattern of alternating cis- and trans-dimers [1] for the adhesive interactions has been proposed. 

In all Figures electrochemical potentials possess clear maxima and minima. Such curve shapes conform to the shape for catalase and electrochemical reactions in the diffusion zone of the system. As mentioned above, molecular oxygen accumulated on the surface of the mimetic electrode during catalase reaction (8.1) diffuses through the adhesive and mimic layers to the electrode surface, where it is activated and interacts with H+. Anions OFT formed in this process may set the electrode surface free for the next portion of oxygen by diffusion only. Thus, the rate of electrochemical reaction (8.2) will be defined by the ratio of the rates of molecular oxygen diffusion to the electrode surface and reverse diffusion of OH- anions from the surface. 

The specific platelet surface receptors that support these initial adhesive interactions are determined by the local fluid dynamic conditions of the vasculature and the extracellular matrix constituents exposed at the sites of vascular injury. Konstantopolous et al. (1998) and Alveriadou et al. (1993) demonstrated that under high shear conditions, the adhesion of platelets to exposed subendothelial surfaces of atherosclerotic or injured vessels presenting collagen and von Willebrand factor (vWF) is primarily mediated by the platelet glycoprotein (GP)Ib/IX/V complex. This primary adhesion to the matrix activates platelets, leading ultimately to platelet aggregation mediated... 

After infection and immune cell activation, endothelial cells are variously activated to bind peripheral blood leucocytes. Bacterial toxins such as lipopolysaccharide (LPS), inflammatory cytokines such as tumour necrosis factors a and (5 (TNFa and TNFP) and interleukin-1 (5 (IL-ip) increase the synthesis of cell surface E- and P-selectins in endothelial cells. Histamine and thrombin increase PM P-selectins in endothelial cells and platelets. L-selectins are constitutively expressed in monocytes and lymphocytes. The selectins are involved in the initial adhesion of leucocytes with endothelial cells via selectin-selectin receptor interactions, for example, monocyte L-selectin-endothelial L-selectin ligand binding and T-lymphocyte-endothelial selectin-integrin interactions. This initial phase of leucocyte-endothelial adhesion enables an early stage of leucocyte rolling through successive formation and breakage of adhesive interactions. 

It has been proposed that cardiac Na channels may be targeted and clustered to specific locations in a similar manner to that observed for Na channels in brain (Cohen 1996). The presence of j subunits in cardiac myocytes may facilitate Na channel locahzation and clustering to discrete functional domains via homophilic or heterophihc cell adhesion interactions. Interestingly, treatment of inside-out patches of ventricular cells with cytochalasin-D induced Na channels to enter a mode characterized by lower peak open probability with a greater persistent activity, consistent with a decrease in the rate of inactivation (Undrovinas et al... 

Fig. 9. Adhesive interactions of the LI glycoprotein. Homophilic interactions between LI glycoproteins on apposing cells A and B form cell-cell contacts. Binding of LI by N-CAM in the same membrane enhances the affinity of homophilic LI interactions. Ll-N-CAM binding may involve a glycan moiety (oligomannosidic-type) of LI and a lectin activity within the fourth Ig-like domain of N-CAM. Adapted from Kadmon et al. [97,98].

Control of adhesion interaction by the addition to adhesives of surface-active substances (surfactants) is of great theoretical and practical interest. The particular effects of siu-factants lie in their ability to decrease the surface tension of the solution due to positive adsorption on the surface. Coating the surface of solid bodies and of liquids with the finest layer of a surfactant added to the system in very small quantities permits changes of the conditions of phase interaction and the progress of the physical-chemical processes. 

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