Blood-Brain Barrier: Evidence for Active Cation Transport between Blood and the Extraceliular Fluid of Brain.

The concentration gradients of Mg(++) and K(+) in the cerebrospinal fluid system indicate that the (Mg(++)) is higher and the (K(+)) is lower in the extra-cellular fluid of the cerebral cortex than the concentrations of these cations in either plasma-dialysate or cisternal fluid. Such cation distribution demonstrates the existence of an active transport process across the blood-brain barrier.