Scanning electron microscopic observations on cells grown in vitro. IV. HeLa cells do not have an upperside-underside polarity.

Small glass particles are added to HeLa monolayer cell cultures. Landing on top of a flattened cell fingerlike protrusions are surrounding the particles. Later on leading lamellae are formed on the upperside of the cell and the glass becomes more and more surrounded until it appears to be "incorporated" completely. The glass particles become attached so firmly that by detaching them the cell surface is destroyed. This speaks against the assumption that cells in monolayers are polarized.