Cells are aware of certain characteristics of their environment and clearly convey preferences. Some cells respond to, for instance, chemicals, light, electric or magnetic fields, temperature, properties of the substratum, or gravity. OK cells, and many other established epithelial lines, demonstrate a distinct predilection for cell-cell contact. Notice, the colony of OK cells featured in this video is initially stretched in an unusual hook-shaped configuration, but the broad lamellipodia of many of the cells seem to reach out in search of other cells in an attempt to fill in the gaps.

The behavior of the cultured cells is thought to be a reflection of their natural behavior in the body. When a wound occurs on the surface of the skin, for example, epithelial cells along the edges of the injured area extend lamellipodia out in an attempt to form a continuous epithelial sheet across the lesion. When the lamellipodia reach other cells and the sheet is successfully produced, the large-scale movements of the cells ceases and specialized junctions are created between the newly adjacent cells. This phenomenon is an excellent example of contact inhibition of migration.

Small membrane-enclosed sac-like structures called vacuoles appear to stream into some of the cells from the edges of their extended lamellipodia. In animal cells, vacuoles are primarily utilized as a means of temporary storage and transport for various materials, such as food, water, and wastes. Since these particular vacuoles form along cell margins, apparently through endocytosis, they presumably contain materials needed by the cell. Most likely the sacs enclose small segments of culture medium, which the cells digest to obtain essential nutrients.