Brain capillary endothelial cells (BCEC) were cultured as an in vitro model of the blood-brain barrier (BBB) and manipulated to investigate how the BBB responds to changes in zinc status. BCEC were grown in minimum essential medium (MEM) with 2% fetal bovine serum and 13% platelet-poor horse serum. A moderate zinc deficiency was imposed by growing the cells in medium containing serums that had previously been dialyzed against EDTA to remove endogenous labile zinc. The control treatment was MEM with undialyzed serums (3 micro mol Zn/L); low-Zn was MEM with dialyzed serums (1.5 micro mol Zn/L); Zn-back was MEM with dialyzed serums, plus ZnCl(2) added back (3 micro mol Zn/L); high-Zn was MEM with undialyzed serums, plus ZnCl(2) (50 micro mol Zn/L). Low-Zn treatment increased (P < 0.02) the rate of zinc uptake into BCEC, relative to control and Zn-back; low-Zn treatment also increased (P < 0.05) the rate of zinc transport across the BCEC into the abluminal chamber (analogous to the brain), relative to control and Zn-back. High-Zn decreased (P < 0.02) the rate of zinc transport across BCEC into the brain, while increasing (P < 0.001) the rate of zinc uptake into BCEC, relative to controls. We conclude that BCEC responded to changes in zinc status by altering the rate of zinc transport in a manner consistent with the BBB actively working to sustain brain zinc homeostasis.