4.1.1. Sample preparation
For time-lapse microscopy, the cells (2–5 103 cells per chamber)
are seeded two days before analysis in an eight-chambered
cover glass (Lab-Tek Chambered #1.0 Borosilicate Cover glass
System, Nunc.) to allow the cells to attach to the bottom and
become flattened so that a better morphological profile can be obtained.
Then cell death is induced. Immediately after adding the
cell death stimulus, place the chambered cover glass in the timelapse
microscope. The cells are imaged using 3D (x, y and z)
time-lapse microscopy with DIC optics. To monitor morphological
changes and membrane permeability in parallel, PI is added to a
final concentration of 3 lM together with the cell death stimulus.
Three-dimensional time-lapse microscopy is performed using a
combination of DIC and epifluorescence optics. The amount of light
to which the cells are exposed should be optimized for each cell
type and for each fluorescent probe in order to reduce phototoxicity
and photobleaching, so that cell death under control conditions
without stimuli is minimized. This means short exposure time, low
lamp voltage, a small number of z-sections and time frames, and
binning of pixels on the CCD camera. Binning allows charges from
adjacent pixels to be combined, which allows shorter exposure
times. The advantage of this technique is that shorter exposure
times are needed because sensitivity increases with the binning
factor, which translates into reduced phototoxicity, but at the expense
of reduced spatial resolution.