Induction of gamma-glutamyl transpeptidase in cultured cerebral endothelial cells by a product released by astrocytes.
gamma-Glutamyl transpeptidase (gamma GTP) is an enzyme found in cerebral capillary endothelial cells, the presumed site of the blood-brain barrier, but not in endothelial cells lining blood vessels in other parts of the body. Using a line of mouse cerebral microvessel endothelial cells (ME-ly cells) and a sensitive colorimetric assay to measure gamma GTP levels we demonstrated that primary cultures of mouse astrocytes and a line of rat C6 glioma cells released a soluble product(s) that induced the production of gamma GTP in cultured endothelial cells by 34% and 39%, respectively, over control levels. Cerebrovascular smooth muscle cells had no significant effect on gamma GTP levels in ME-ly cells, and the astrocyte product(s) had no effect on rabbit aortic endothelial cells. The induction of gamma GTP levels in ME-ly cells was apparent after one day of exposure to the astrocyte product(s) and increased in magnitude with increasing time of exposure of the ME-ly cells to the product(s). Removal of the product(s) from the ME-ly cells resulted in a return to control levels of gamma GTP in the ME-ly cells within 2 days. The presence of a protein synthesis inhibitor during incubation with the product(s) blocked the induction of gamma GTP in ME-ly cells, and treatment of the product(s) with 200 U/ml TPCK-trypsin destroyed its inductive properties.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D001921:Brain / Q000098:blood supply* / Q000201:enzymology; D002196:Capillaries / Q000166:cytology / Q000201:enzymology; D002478:Cells, Cultured; D003470:Culture Media; D004727:Endothelium / Q000201:enzymology*; D051379:Mice; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D011817:Rabbits; D051381:Rats; D013997:Time Factors; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D003470:Culture Media; D005723:gamma-Glutamyltransferase