Characterization of a gamma-glutamyl transpeptidase positive subpopulation of endothelial cells in a spontaneous tube-forming clone of rat cerebral resistance-vessel endothelium.

A spontaneous tube-forming clone of rat cerebral resistance-vessel endothelium was characterized in long-term serial culture. In this study, a clone, RV-150 ECT, of cerebral resistance vessel endothelial cells in long-term culture has been shown to have a subpopulation of gamma-GTP positive cells that are present in all cultures regardless of confluency status or tube-forming stages. In pre-confluent and confluent cultures, the gamma-GTP positive cells are few in number, stain weakly, and are randomly distributed in the monolayers. In monolayer post-confluent cultures, gamma-GTP positive cells increase in number, stain strongly, and begin to show signs of non-random distributions. In early post-confluent cultures that have become a mixture of monolayer and multilayer cells, there is a further increase in gamma-GTP positive cells which begin to form distinct groupings. In mid post-confluent cultures, the multilayered areas of the culture have begun clustering to form clear multicellular aggregates. The gamma-GTP positive cells at this stage are reduced in number and are predominantly associated with the cell clusters. In late post-confluent cultures, the multicellular clusters develop clear cell cords between/among the clusters. At this stage the gamma-GTP positive cells are associated exclusively with cell clusters. With cord development, the gamma-GTP positive cells are associated with both clusters and cords, and are reduced in number apparently because of selective degeneration of these cells. The results of this study demonstrate that a phenotypically distinct subpopulation of endothelial cells exhibits characteristic features of the blood-brain barrier, namely gamma-GTP. The ability of these cells to express this property in long-term serial culture suggests that this may represent a useful in vitro model to study the growth and differentiation of blood-brain barrier vessels.