Figure 2

Depolarization increases binding of annexin V to cells with exposed PS. Jurkat cells were left untreated (Panel A) or were exposed to UV light to induce apoptosis (Panel B). After 3.5 h, cells were assayed by flow cytometry with fluorescein-annexin V-117. Most of the UV-treated cells have entered the apoptotic pathway and have exposed PS on the extracellular face of the plasma membrane, as indicated by the development of a sizable population of annexin-positive cells. Depolarization with high-potassium Buffer B (solid lines) increases the mean fluorescence intensity of annexin-positive cells about 41% compared to results obtained in low-potassium Buffer A (dashed lines). However, depolarization does not alter the mean fluorescence of the annexin-negative population in either untreated or UV-treated cells. The horizontal bars in the lower part of Panel B indicate the gates used to define the annexin-negative and annexin-positive cell populations to allow calculation of mean fluorescence intensities for these cell populations. Panel C: Forward-scatter histograms for untreated cells or UV-treated cells. The horizontal line indicates the gate used to define the shrunken cells that are observed only in apoptosis. Panel D: Annexin V histograms for the shrunken apoptotic cells assayed in low-potassium A buffer (dashed lines) or high-potassium B buffer (solid lines). Depolarization increases annexin V binding to this population by about 83%.