Manganese Distribution Across the Blood–Brain Barrier III: The Divalent Metal Transporter-1 is not the Major Mechanism Mediating Brain Manganese Uptake

Abstract

Manganese (Mn) is essential for and toxic to the brain. Brain Mn uptake utilizes both diffusion and transporter-mediated pathways. The divalent metal transporter-1 (DMT-1) has been suggested to mediate brain Mn uptake. The b/ b Belgrade rat does not express significant amounts of functional DMT-1. In the present work, brain influx transfer coefficients of 54 Mn ion and 54 Mn transferrin (Mn Tf) were determined in b/ b and +/ b Belgrade and Wistar rats using the in situ brain perfusion technique. Brain Mn uptake was not significantly different among the three rat strains for either Mn species. We hypothesized that Mn may enter brain endothelial cells by a DMT-1-independent process but not be able to distribute across those cells into brain tissue due to the absence of DMT-1 activity. To test this hypothesis the brain capillary endothelial cells were isolated from b/ b and +/ b Belgrade rats and Wistar rats after in situ brain perfusion. Some animals received cerebrovascular washout after in situ brain perfusion to ascertain any affect of genotype on 54 Mn adsorption to the endothelial cell luminal surface. Less than 30% of the brain 54 Mn after 54 Mn ion or 54 Mn Tf perfusion remained associated with endothelial cells, suggesting the majority had distributed into brain extracellular fluid (ECF) and/or brain cells. Mn appears to distribute across the rat blood–brain barrier (BBB) into the brain by one or more carrier-mediated processes other than the DMT-1.