Each bovine pulmonary artery endothelial cell exhibits one or more nuclei, each of which contains rounded nucleoli, and is surrounded by many small mitochondria. The mitochondria exhibit a granular appearance when observed with a light microscope, a fact that was noted by the nineteenth century microscopists who first identified the organelles and coined their name from the Greek words mitos and khondrion, respectively meaning “thread” and “granule.” The larger, spherical structures that appear in the cytoplasm of the cells (especially in several that are along the bottom of the field of view early in the time-lapse sequence) are vacuoles, membrane-bound sacs formed for the temporary storage of food, water, or wastes.

During the high speed playback of the time-lapse sequence, there seems to be sudden activity along the edges of some of the BPAE cells that gives the impression of a flickering light. The phenomenon, known as ruffling, involves the rapid formation and retraction of lamellipodia and other surface extensions. Notice little ruffling occurs along overlapping cell margins. Such activity is generally most pronounced along the free edges of cells since cell-cell junctions can interfere with the extension of surface structures.

Several BPAE cells can be observed undergoing mitosis. The resultant daughter cells generally establish their own polarity and begin migrating along their own paths soon after the process takes place. Occasionally, however, a bridge of cellular material between the two cells remains for some time, before it finally becomes stretched too thin and breaks as the endothelial cells advance further and further apart.