Fig. 10.

Model of ENT-mediated transport of nucleosides across the BTB. The illustration of the seminiferous tubule and surrounding cells depicts how nucleosides could be transported into the lumen via ENT transporters. ENT1 is the primary transporter responsible for uptake of nucleosides into the Sertoli cells owing to the higher concentration of nucleosides in the blood. ENT2 is proposed to play a role in efflux of nucleosides into the lumen of the seminiferous tubules because of the higher concentration of intracellular nucleosides (mediated by ENT1) compared with the lumen of the seminiferous tubule.