Phenotypic changes in mitochondrial membrane potential (Δψm) during valinomycin-induced depolarisation and apoptosis

A large body of evidence has implicated mitochondria in control of cell death, where key apoptotic mechanisms involve change in mitochondrial membrane permeability and depolarisation of mitochondrial membrane potential (Delta psi(m)). Assessment of Delta psi(m) is traditionally conducted using the lipophilic cation JC-1 on the flow cytometer or by fluorescent microscopy. Here we assess JC-1 aggregation using the novel tool of digital texture analysis to establish mitochondrial phenotypic changes induced by the K+ ionophore, valinomycin in a unique model comprising SW480 and SW620 cell lines. This provides an opportunity to study these phenomena in the context of colorectal cancer. Valinomycin-induced apoptosis was detected using morphology and analysis of DNA content. Cells were treated with valinomycin, images digitally recorded on a calibrated video photometer and subjected to high resolution digital texture analysis. This demonstrated that the HARAM texture features (Mean of the Haralick texture features) were highly valuable in describing the transition of Delta psi(m) as the cell undergoes apoptosis. In conclusion this study illustrates the potential of texture analysis as a novel and additional technique for quantifying JC-1 aggregation and revealing the spectrum of collapse of Delta psi(m) during apoptosis.