Fig. 4. Differentiating annexin V-binding C2C12 (A1,A2) and H9C2 (B1-3) myoblasts have an intact plasma membrane as detected by PI exclusion. In all cultures low numbers of solitary annexin V (green) and PI (red) labeled cells were found (A1,B1,B3, arrows). These postapoptotic/necrotic cells can clearly be discriminated from annexin V-positive differentiating myoblasts where annexin V labeling is preferentially located at cell-cell contact areas (A2, nuclei stained with DAPI; B2, asterices indicate location of nuclei), and which are PI impermeable (A2,B2,B3, asterisks indicate location of nuclei). In-between the cells shown in B2, an annexin V- and PI-positive cell fragment, most probably resulting from apoptotic cell membrane blebbing, is present (arrowhead). Bars, 25 µm (A1,A2,B1,B2); 200 µm (B3).