At a recent lecture on apoptosis, the hypothesis was put fourth that cell volume accompanied by ion changes were the very significant and initial events during apoptosis in lymphoid cells. It was suggested that these changes came prior to caspase changes, mitochondrial changes, membrane potential changes and nuclear fragmentation. 1. What is the current thinking regarding the sequential events in the apoptosis process that can be detected by fluorescent-based assays like flow cytometry? 2. After the lecture, I asked the speaker the question regarding the capability of a flow cytometer to detect early size changes using light scatter. Does the flow cytometer have a sufficient sensitivity to measure early volume changes by light scatter? What is the percentage decrease in cellular volume that would be necessary to effectively make the conclusion that cell volume size changes are the initial event in the apoptosis pathway? The speaker did not think this was a relevant question and felt it was only a technical question in which the operator of the equipment could easily answer. In my opinion in order to prove the hypothesis that cell volume is indeed an initial event in the apoptosis pathway, one has to understand how effective the flow cytometer will be in determining early size changes using the light scatter parameters. Can small changes in light scatter be detected early in the apoptosis process and thus be used as an initial measurable flow cyotmetric event in the apoptosis pathway? Bob Robert M. Zucker, PhD U.S. Environmental Protection Agency Office of Research and Development National Health and Environmental Effects Research Laboratory Reproductive Toxicology Division, MD 72 Research Triangle Park, North Carolina, 27711 Tel: 919-541-1585; fax 919-541-4017 e-mail: zucker.robert@epa.gov
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