Characterization of a γ‐glutamyl transpeptidase positive subpopulation of endothelial cells in a spontaneous tube‐forming clone of rat cerebral resistance‐vessel endothelium

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Abstract
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 γ‐GTP positive cells that are present in all cultures regardless of confluency status or tube‐forming stages. In pre‐confluent and confluent cultures, the γ‐GTP positive cells are few in number, stain weakly, and are randomly distributed in the monolayers. In monolayer post‐confluent cultures, γ‐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 γ‐GTP positive cells which begin to form distinct groupings. In mid post‐confluent fultures, the multilayered areas of the culture have begun clustering to form clear multicellular aggregates. The γ‐GTP positive cells at this stage are reduced in number and are predominately associated with the cell clusters. In late postconfluent cultures, the multicellular clusters develop clear cell cords between/among the clusters. At this stage the γ‐GTP positive cells are associated exclusively with cell clustters. With cord development, the γ‐GTP positive cells are associated with bothe 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 γ‐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 bloodbrain barrier vessels.