MANGANESE (MN) TRANSPORT ACROSS THE RAT-BLOOD BRAIN BARRIER - SATURABLE AND TRANSFERRIN-DEPENDENT TRANSPORT MECHANISMS

Using a single capillary pass technique, the transport of manganese (M n) across the rat blood-brain barrier (BBB) was characterized. Initial rate measurements (15 s) of Mn2+ [0-1000 muM] accumulation in rat bra ins clearly indicated saturation kinetics by both 1/v vs. 1/s plots, a nd plots of v vs. [s]. Common carotid injection of freshly mixed Mn2with transferrin at a 1:10 molar ratio did not result in a significant change in the initial rate of Mn brain levels compared with injection of Mn2+ alone. However, when Mn2+ was incubated at 25-degrees-C in th e presence of transferrin at a 1:10 ratio for up to 5 days prior to co mmon carotid injection, the initial rate of Mn uptake by brain was inc ubation-time-dependent, increasing linearly with prolonged incubations . These findings suggest that the saturable component of divalent Mn t ransport into brain represents but one of the transport mechanisms for Mn across the BBB. A second transport system for Mn may occur by a tr ansferrin-conjugated Mn transport system.