Surface view of pericytes on the retinal capillary in rabbits revealed by scanning electron microscopy.

Retinal capillaries of the rabbit were treated with HCl and collagenase to visualize the pericytes attached to the stromal surface of the capillary walls under the scanning electron microscope. Two types of pericytes were distinguishable on the basis of shape and localization. One type (Type I) had a slightly bulged, fusiform cell body with a few, long, branching cytoplasmic processes, and these cells were scattered mainly in the region of the true capillary. The other type (Type II) possessed a rather flattened and polymorphic cell body from which radiated short irregular cytoplasmic processes, and these cells, which tended to overlap more or less, were present predominantly in the region of the pre- or postcapillary vessels in the capillary bed. The latter type cells were assumed to be precursors of the smooth muscle cells.