A comparative study of U937 cell size changes during apoptosis initiation by flow cytometry, light scattering, water assay and electronic sizing

When the body loses water, the fluid outside cells becomes more concentrated, pulling water out of cells and causing them to shrink.

When U937 cells enter late-stage apoptosis, they shrink in volume, which causes a measurable drop in forward light scatter, and this change consistently occurs alongside annexin V binding, regardless of how the cell death was triggered.

In U937 cells, a change in cell water content caused by certain chemicals increases forward light scatter, but cell death caused by another chemical without water loss does not increase forward light scatter, showing that water content directly determines this optical signal.

In U937 cells undergoing apoptosis, the pattern of light scatter changes differently depending on how apoptosis is triggered: agents that cause cell dehydration produce a two-phase light scatter response, while agents that do not cause dehydration produce only the second phase.

In human lymphoid cells undergoing apoptosis, forward light scatter increases when cells lose water, but not when they shrink without losing water. This means the change in light scatter depends on hydration, not just cell size.

In U937 cells undergoing early apoptosis, changes in forward light scatter detected by flow cytometry do not reliably reflect cell volume reduction because water content changes in the cells alter the signal in ways that contradict volume changes.