Junctional transfer of small molecules in cultured bovine brain microvascular endothelial cells and pericytes

We have utilized cultures of bovine brain microvascular endothelial cells (MEC) and pericytes to study two aspects of intercellular relations in the microvasculature. First, the apparent contradiction between the reported demonstration of dye transfer between endothelial cells in capillaries and venules in rat omentum and the lack of ultrastructurally demonstrable interendothelial gap junctions in the same vessels in omentum, brain, and other tissues led us to examine this problem in vitro. MEC showed extensive transfer of both fluorescent dye (Lucifer yellow CH, 96% transfer incidence in primary culture) and radiolabeled uridine nucleotides (97%). Freeze-fracture replicas of MEC revealed both gap and tight junctions. These results demonstrate that MEC are capable of producing gap junctions and engaging in junctional communication in vitro. Second, we have examined the interaction of pericytes with MEC. Cultured pericytes showed gap junctions in freeze-fracture replicas, variable dye transfer (cell density dependent, 19-91%), and extensive nucleotide transfer (94%). While the incidence of dye transfer between MEC and pericytes was low (10-31%), nucleotide transfer between these cells was extensive (86-96%). The demonstration of junctional transfer between MEC and pericytes in vitro may be particularly significant considering the high frequency of junctional contact between these cells in vivo. These cultured cell models should help us to better understand the complex interactions of vessel wall cells in microvascular physiology and pathophysiology.