A novel method to determine the localization of high and low-affinity GABA transporters to the luminal and antiluminal membranes of brain capillary endothelial cells

Some evidence has shown that the luminal plasma membrane and the antiluminal plasma membrane of the blood-brain barrier (BBB) are functionally distinct. This polarity permits brain capillary endothelial cells (BCECs) to actively regulate the internal milieu of the brain. Especially, polarity also exists concerning the transport of some endogenous substances such as amino acids and glucose. It is important to determine the luminal and antiluminal membrane localization of some transporters of endogenous substances, which will contribute to a better understanding of the transport mechanisms of the endogenous substances at the BBB. The present paper describes a novel procedure for combining isolated brain capillaries with primary cultured BCECs to determine the subcellular localization of some transporters, which is relatively simpler than the methods described previously. This method was used for the first time to determine successfully the luminal and antiluminal distribution of high and low-affinity GABA transporters. The low-affinity GABA transporter is probably localized to the luminal membrane of BCECs, and the high-affinity GABA transporter may be localized to the antiluminal membrane.