Cation transport specificity at the blood-brain barrier

The molecular identification, expression and cloning of membrane-bound organic cation transporters are being completed in isolated in vitro membranes. In vivo studies, where cation specificity overlaps, need to complement this work. Cross-inhibition of [3H]choline and [3H]thiamine brain uptake by in situ rat brain perfusion. [3H]Choline brain uptake was not inhibited by thiamine at physiologic concentrations (100 nM). However, choline ranging from 100 nM to 250 microM inhibited [3H]thiamine brain uptake, though not below levels observed at thiamine concentrations of 100 nM. (1) The molecular family of the blood-brain barrier (BBB) choline transporter may be elucidated in vitro by its interaction with physiologic thiamine levels, and (2) two cationic transporters at the BBB may be responsible for thiamine brain uptake.