Cell death in the posterior necrotic zone of the developing chick wing measured by the loss of membrane integrity

Cell death in the posterior necrotic zone (PNZ) of the developing chick wing was examined in organ culture using a 51 chromium release assay. This isotope is incorporated into the cytoplasm of mesenchymal cells and is released from the tissue very slowly. A sudden increase in 51 Cr release coincides with cell death and lysis. There is no evidence of an increase in membrane permeability prior to histological evidence of cell lysis. Lysis begins at late stage 22 or early stage 23 and lasts for 9 hours. Approximately 3,500 cells lyse in the PNZ during this period of time, resulting in a considerable decrease in cell density in the tissue.