ZINC TRANSPORT ACROSS AN IN-VITRO BLOOD-BRAIN-BARRIER MODEL

The influence of plasma zinc concentration on the rate of zinc transpo rt into the brain was examined using an in vitro model of the blood-br ain barrier. The model was constructed by culturing porcine brain capi llary endothelial cells on porous membrane filters suspended between t wo chambers of fluid, representing the capillary lumen and the cerebro spinal fluid of the brain. A relatively narrow range of zinc concentra tions (2-30 mu mol/L) was employed in order to examine the most physio logicarlly relevant situation, obtained by diluting the serum or addin g ZnCl2. The results consistently found that the rate of zinc transpor t across the blood-brain barrier was similar (P >.05) between 10 and 2 6 mu mol zinc/L; the rate was slower (P <.05) at zinc concentrations b elow 7 mu mol/L and faster (P <.05) above 30 mu mol zinc/L. These resu lts demonstrate that the blood-brain barrier is highly restrictive to zinc. Zinc enters the brain at a constant rate within the range of pla sma zinc concentrations that occur in healthy individuals. Outside thi s range, zinc transport was significantly altered. The zinc transport process was highly selective for zinc, since none of the analogous min erals could effectively compete with it. The zinc transport process do es not require energy, since metabolic inhibitors did not influence th e transport rate. (C) 1997 Wiley-Liss, Inc.