Stressful levels, cell response

In both plant (e.g. [57]) and animal (e.g. [86]) cell systems, cellular respiration has been shown to be a more sensitive indicator of system response to hydro-dynamic stress than membrane integrity, suggesting that intracellular enzymes and/or organelles may be affected at stress levels lower than those required to cause membrane damage. 

Lack of precision. The complex nature of any biological system, be it an entire animal or individual cell, often results in the responses observed being influenced by factors such as metabolic status of individual cells, or (in the case of whole animals) subclinical infections, stress levels induced by human handling, etc. 

With modest increase in intracellular ROS levels, activation of NF-kB takes place, which protects the cell against oxidative stress [45], Direct root of ROS participation in signal transduction from cell membrane to intracellular metabolic reactions were recently described. Among them - activation of potential-dependent K-channels and variation of membrane potential, inhibition of cellular protein phosphatases and restriction of activity of MAP-kinase [49]. Such view on intracellular role of ROS consider them as second messengers, which together with cyclic nucleotides, calcium ions, and other biologically active compounds provides adequate cell response to the outer signals. 

Apoptosis is found to proceed in different cells at different times after an initial stress is applied. However, the current experimental measurements on apoptotic processes in particular cells are typically performed on large cell populations. Such experiments necessarily lead to measurements of an inhomogeneous distribution of cell responses. Therefore, it is particularly attractive to be able to carry out external perturbations at the single-cell level. 

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