title: Multidrug resistance-related transport proteins in isolated human brain microvessels and in cells cultured from these isolates.
abstract: The multidrug transporter, P-glycoprotein (Pgp), at the blood-brain barrier is thought to be important for limiting access of toxic agents to the brain, but controversy surrounds its cellular location, whether on endothelium or on adjacent astrocyte foot processes. In the present study, the distribution of protein and mRNA for Pgp and for another transporter, multidrug resistance-associated protein (MRP), is compared with that for the endothelial marker, platelet-endothelial cell adhesion molecule-1 (PECAM-1) and for the astrocyte-derived glial fibrillary acidic protein (GFAP) in microvessels isolated from human brain and in cells grown from these microvessels. Activities of the multidrug transporters are assessed in the cultured cells from the effects of transport inhibitors on intracellular [3H]vincristine accumulation. The isolated microvessels show strong immunocytochemical staining for Pgp and PECAM-1 and little or no staining for GFAP and MRP, and they contain mRNAs detectable by RT-PCR encoding only Pgp and PECAM-1, but not GFAP or MRP. Thus, Pgp may well be synthesised and expressed on cells within the microvessels rather than on adherent astrocyte foot processes. In cells grown from the microvessels, although PECAM-1 remains, Pgp expression decreases and MRP appears. Evidence suggests these multidrug transporters are functionally active in the cultured cells.
authors.affiliation: Department of Pharmacology, University of Cambridge, England, UK.
authors.forename: S
authors.initials: S
authors.lastname: Seetharaman
authors.forename: M A
authors.initials: MA
authors.lastname: Barrand
authors.forename: L
authors.initials: L
authors.lastname: Maskell
authors.forename: R J
authors.initials: RJ
authors.lastname: Scheper
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000032:analysis* / Q000235:genetics / Q000276:immunology; D000818:Animals; D000918:Antibody Specificity; D001253:Astrocytes / Q000737:chemistry; D001812:Blood-Brain Barrier; D001921:Brain / Q000098:blood supply*; D002196:Capillaries / Q000737:chemistry / Q000166:cytology; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000737:chemistry; D015870:Gene Expression; D005904:Glial Fibrillary Acidic Protein / Q000032:analysis; D006801:Humans; D008297:Male; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000032:analysis* / Q000235:genetics / Q000276:immunology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D014750:Vincristine / Q000493:pharmacokinetics*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D005904:Glial Fibrillary Acidic Protein; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D012333:RNA, Messenger; D014750:Vincristine