Early cells internal flows

One of the early apoptotic events is exposure of phosphatidylserine normally present in the inner leaflet of the plasma membrane to the outer leaflet otherwise known as the phosphatidylserine flip (PS-flip) (27,28). Detection of the PS-flip is possible using annexin V, a 35 kDa protein with a high affinity for phosphatidylserine. Because of the nature of the PS-flip, annexin V is most useful in studying intact cells such as in flow cytometry or confo-cal microscopy. Cells in fixed tissue sections are not intact and use of labeled annexin V would not be able to differentiate between internal and external phosphatidylserine, though at least one investigator has attempted to circumvent this problem (29). 

In the early days of tuneable diode laser spectroscopy, as is true for many modem-day applications, the experimental set-up of a TDLAS system was comprised of a gas cell as its centrepiece. This sampled the analyte across a closed volume allowing for the control of the internal and external parameters (e.g. ambient temperature, gas pressure in the cell, etc.). Then, flow-type systems were introduced later, in which the overall configuration was modified so that the gas could be continuously exchanged in a flow through the cell, normally assisted by a pump at the exit of the cell, as shown in Section 28.2. 

---