ABSTRACT
An individual cell is exposed to a large number of environmental stimuli that initiate complex interconnecting intracellular signaling cascades, which in turn modulate a dynamic community of intracellular proteins. Stimuli may act through binding to specific receptors on the cell surface. Such ligand-receptor interactions include receptor binding of hormones, growth factors, neuropeptides, and specific amino acid sequences found in the extracellular matrix (e.g., arginine-glycine-aspartic acid, also termed RGD). Cells can also be greatly influenced through interaction with factors that are nonspecific in that they do not require membrane-associated receptors. An example of such a factor is provided by antimicrobial defense peptides that form multimeric pores in cell membranes and can serve as trophic factors over a narrow range of concentrations while inducing toxicity at high concentrations. Finally, cells are also impacted by numerous nonspecific environmental factors, such as pH, osmolality, temperature, ion concentrations, electrical fields, surface chemistry of the substratum, and biomechanical stressors. How a cell assimilates and responds to a multitude of simultaneous stimuli is still largely unknown.
