Junction functionality

Obviously, universal constant, cj) depends on the number of chains that are linked at a crosslink (junction functionality f) and probably on the chemical composition as well. 

Comparison with Eq. (3.1) reveals that the influence of the junction functionality f is neglected in this simplified treatment. Such a simplification is doubtful for f = 3. 

The structure of a perfect network may be defined by two variables, the cycle rank and the average junction functionality (f>. Cycle rank is defined as the number of chains that must be cut to reduce the network to a tree. The three other parameters used often in defining a network are (i) the number of network chains (chains between junctions) v, (ii) the number of junctions p, and (iii) the molecular weight Mc of chains between two junctions. They may be obtained from and using the relations... 

Equation (40) shows that the small deformation shear modulus of an affine network increases indefinitely over the phantom network modulus as junction functionality approaches 2. 

Equilibrium Tensile Behavior of Model Silicone Networks of High Junction Functionality... 

Elastomeric networks with junction functionalities ranging from 4 to 70 were prepared by endlinking a,u)-divinyl poly(dimethylsiloxane) chains having number average molecular weights ranging from 8,800 to 55,300 with polyfunctional junctions provided by linear and branched poly(methylhydrogensiloxanes). 

Junction Functionality. Some results bearing on the possible effect of cross-link functionality on the upturn in modulus are shown in Figure 5(20). The magnitude of the increase in [f ] does not show any obvious correlation with , which again suggests the predominant importance of the intramolecular characteristics of the short chains. At least from the evidence at hand (20), the functionality of the junction points seems relatively unimportant in this regard. 

Clarke H, Marano CW, Soler AP, and Mullin JM [2000] Modification of tight junction function by protein kinase-C isoforms. Adv Drug Deliv Rev 41 283-301... 

The immunohistochemical findings were correlated with reduced intercellular coupling indicating a possible role of disturbed Cx43 expression and gap junction function in the pathogenesis of Chagas disease and the arrhythmias associated with that disease. 

As already described, the upper three portions of Figure 2 summarize the differences in the way the constraints are applied in the constrained-junction theory, constrained-chain theory, and the diffused-constraints theory, respectively [4], Additional comparisons between theory and experiment for a variety of elastomeric properties should be very helpful [20], Also, neutron-scattering measurements conducted on series of networks having different values of the junction functionality , which is the number of chains emanating from a junction (cross-link), would be extremely useful in suggesting how to position the constraints along a chain in refining such models, since should have a pronounced effect on the... 

Synapses are electrical or chemical communicative contacts between neurons. Electrical synapses (neuronal gap junctions) function by the propagation of electrical impulses from one cell to another (and vice versa) via direct, physical contact. As a consequence, these synapses are characterized by a relatively simple organization of membrane structure and associated organelles (Zoidl et al. 2002). Electrical synapses are also less mutable, in terms of their function and molecular characteristics, and thus exhibit little of the plasticity that typifies the chemical synapse. 

Brown RC, Davis TP (2002) Calcium modulation of adherens tight junction function A potential mechauism for blood-brain banier disruption after stroke. Stroke 33 1706-1711. 

Figure 5 Cellular/tissue functions linked to gap junction function.

Epigenetic Toxicity as a Resuit of inappropriate Moduiation of Gap Junction Function... 

Figure 6 Disease states correlated with defective gap junction function.

Figure 8 Use of the scrape loading/dye transfer assay to screen for agents that can prevent inhibition of gap junction function.

Of the three types of anchoring junctions present In epithelial cells, two participate In cell-cell adhesion, whereas the third participates In cell matrix adhesion. Adherens June tions, which connect the lateral membranes of adjacent epithelial cells, are usually located near the apical surface, just below the tight junctions (see Figures 6-1 and 6-5). A circumferential belt of actin and myosin filaments In a complex with the adherens junction functions as a tension cable that can Internally brace the cell and thereby control Its shape. 

Classical approaches to verification of functional gap junctions include conductance measurement, pharmacological manipulation, and demonstration of dye coupling (28). Dye coupling is a straightforward method for demonstrating gap junctional function. Injection experiments are simple and results are easily interpreted. The outcome is assessed immediately with an in vivo preparation. A lower dye concentration is necessary for detection because dye lost during fixation and tissue processing is avoided. 

Using both condensation-cured and addition-cured model systems, it has been shown that the modulus depends on the molecular weight of the polymer and that the modulus at rupture increases with increased junction functionality (259). However, if a bimodal distribution of chain lengths is employed, an anomalously high modulus at high extensions is observed. Finite extensibility of the short chains has been proposed as the origin of this upturn in the stress—strain curve. 

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