Charged extracellular matrix

The use of plastic materials for routine cell culture on the laboratory scale was introduced at the end of the 1960s, and some characteristics of glass surface, such as hydrophobicity and negative charge, were maintained in these materials. Polystyrene is the most widely used plastic material for animal cell adhesion at present, because of its surface characteristics, its low cost, and also its transparency. For more demanding cell lines, the surface has to be submitted to a treatment that involves coating with proteins such as poly-lysine, poly-ornithine, or extracellular matrix-derived proteins such as fibronectin, laminin, and collagens. 

Elastin is a macromolecule synthesized as a 70,000 single peptide chain, termed tropoelastin and secreted into the extracellular matrix where it is rapidly crosslinked to form mature elastin. The carboxy-terminal end of elastin is highly conserved with the sequence Gly-Gly-Ala-Cys-Leu-Gly-Leu-Ala-Cys-Gly-Arg-Lys-Arg-Lys. The two Cys residues that form disulfide crosslinks are found in this region as well as a positively charged pocket of residues that is believed to be the site of interaction with microfibrillar protein residues. Hydrophobic alanine-rich sequences are known to form a helices in elastin these sequences are found near lysine residues that form crosslinks between two or more chains. Alanine residues not adjacent to lysine residues found near proline and other bulky hydrophobic amino acids inhibit a helix formation. Additional evidence exists for (3 structures and 3 turns within elastin thereby giving an overall model of the molecule that contains helical stiff segments connected by flexible segments. 

An intrinsic ionic charge gradient across the membrane exists because of semipermeable nature of membrane, which maintains a difference in the concentration of the ions between the cytosol and the extracellular matrix. This difference results in a definite potential across membrane of the normal cells, which is called the resting potential. Normal plant cells, mammalian muscle cells, and neurons have resting potential values of about —120, —90, and —70 mV, respectively. Along with the resistance to the flow of ions, membrane also exhibits a capacitance. Cm, which is given by... 

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