Figure 4.

Chemoprotective and endogenous molecule transporters of the invertebrate BBB. The transcellular chemoprotective barrier is primarily provided by the ATP-binding Cassette (ABC) transporters. These xenobiotic efflux transporters are localized to the apical surface of the subperineurial glia (SPG) and remove lipophilic molecules from the SPG membrane, preventing access to the brain. Members of the Solute Carrier (SLC) class of transporters also have some chemoprotective roles, but are mainly known as transporters of endogenous molecules. The SLCs control the entry of hydrophilic/charged molecules (e.g., glucose, amino acids and ions) into the brain, to support optimal brain function. SLCs are present both on the apical and basal surfaces of the SPG cells. Some SLC members, e.g., Oatp58Dc, are also expressed in the perineurial glia (PG). Red and white hexagons represent xenobiotics and endogenous molecules, respectively. NL, neural lamella; CNS, central nervous system.