Three-dimensional ultrastructural distribution of cytoplasmic interdigitation between endothelium and pericyte of capillary in human granulation tissue by serial section reconstruction method.

Two- and three-dimensional electron microscopic observations in the capillaries with angiogenetic sprout of human granulation tissue revealed the cytoplasmic interdigitations (CID) between the endothelium and the pericyte, which were composed of unit of cytoplasmic projection and an indentation. Two types of interdigitation were observed: the interdigitation composed of cytoplasmic projection from the pericyte plugging into the endothelial indentation, CID(P-E); the interdigitation which had a reverse mode of composition of the cytoplasmic projection and indentation to the former one, CID(E-P). We investigated three-dimensional distribution of the two kinds of interdigitation in two cases of the capillaries with angiogenetic sprout. The two kinds of interdigitation exhibited a remarkable difference in the three-dimensional distribution. The CID(P-E) was rather uniformly distributed over the parent capillary endothelial area (6.4 per endothelium in average) and was not observed at all in the angiogenetic area; the other type of cytoplasmic interdigitation, CID(E-P), was located in only the angiogenetic sprouting endothelial area (3.5 per endothelium in average). The cytoplasmic interdigitation between the endothelium and the pericyte in vivo was the only site for cell contact and seemed to be involved in a conducting function which is biochemically proved to exist in vitro between the two cells.