SATURABLE TRANSPORT OF MANGANESE(II) ACROSS THE RAT-BLOOD BRAIN BARRIER

Unanesthetized adult male rats were infused intravenously with solutions containing Mn-54 (II) and one of six concentrations of stable Mn(II). The infusion was timed to produce a near constant [Mn] in plasma for up to 20 min. Plasma was collected serially and on termination of the experiment, samples of CSF, eight brain regions, and choroid plexus (CP) were obtained. Influx of Mn (J(Mn)) was calculated from uptake of Mn-54 into tissues and CSF at two different times. Plasma [Mn] was varied 1,000-fold (0.076-78 nmol/ml). Over this plasma concentration range, J(Mn) increased 123 times into CP, 18-120 times into brain, and 706 times into CSF. CP and brain J(Mn) values fit saturation kinetics with K(m) (nmol/ml) equal to 15 for CP and 0.7-2.1 for brain, and V(max) (10(-2) nmol . g-1 . s-1) of 27 for CP and 0.025-0.054 for brain. Brain J(Mn) except at cerebral cortex had a nonsaturable component. CSF J(Mn) varied linearly with plasma [Mn]. These findings suggest that Mn transport into brain and CP is saturable, but transport into CSF is nonsaturable.