Donepezil, tacrine and α-phenyl-n-tert-butyl nitrone (PBN) inhibit choline transport by conditionally immortalized rat brain capillary endothelial cell lines (TR-BBB)

In the present study, we have characterized the choline transport system and examined the influence of various amine drugs on the choline transporter using a conditionally immortalized rat brain capillary endothelial cell line (TR-BBB) in vitro. The cell-to-medium (C/M) ratio of [³H]choline in TR-BBB cells increased time-dependently. The initial uptake rate of [ ³H]choline was concentration-dependent with a Michaelis-Menten value, K_m, of 26.2 ± 2.7 μM. The [³H]choline uptake into TR-BBB was Na⁺-independent, but was membrane potential-dependent. The [³H]choline uptake was susceptible to inhibition by hemicholinium-3, and tetraethylammonium (TEA), which are organic cation transporter substrates. Also, the uptake of [³H]choline was competitively inhibited with K_i values of 274 μM, 251 μM and 180 μM in the presence of donepezil hydrochloride, tacrine and α-phenyl-n-tert-butyl nitrone (PBN), respectively. These characteristics of choline transport are consistent with those of the organic cation transporter (OCT). OCT2 mRNA was expressed in TR-BBB cells, while the expression of OCT3 or choline transporter (CHT) was not detected. Accordingly, these results suggest that OCT2 is a candidate for choline transport at the BBB and may influence the BBB permeability of amine drugs.