Excitement metabolic signals

The existence of an activator may be anticipated in the neighborhood of a Hopf bifurcation. Here the system is either excitable or oscillatory. Such excitable and oscillatory domains exist on many levels of biological organization - on the genetic, metabolic, signal transduction and neuronal levels. Hence one may expect to find the kinetic conditions for the DIFICI fulfilled in many such circumstances. The conditions for the DIFIRI seem to be even less restrictive. 

The maintenance of both the membrane potential and the steep gradients of ionic concentrations is essential to cells, both as a means of coupling metabolic energy to transport and other processes and for electrical signaling. The effects are most pronounced for mitochondrial membranes for which Em may attain -140 to -170 mV and for plasma membranes of excitable cells such as neurons (Em = -70 to -90 mV). For liver and kidney cells Em of plasma membranes maybe approximately - 35 mV and for erythrocytes only -9 mV.480... 

Non-excitable cells with no obvious electrical activity play the same important role as excitable cells in cell-based biosensors. The changes in electrical signals, such as cell impedance, and nonelectrical parameters such as cell morphology, proliferation, metabolism, cell viability, pH, and extracellular analyte concentrations, can be measured upon chemical exposure and physical stimuli. Cells can also be genetically engineered to express reporters or biomarkers, such as the green fluorescence protein (GFP), upon specific stimulation. 

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