The concentrative nucleoside transporter (CNT) family comprises three members: CNT1, CNT2 and CNT3. CNT2 participates in the absorption and disposition of endogenous nucleosides and mediates the first step of nucleotide biosynthesis. CNT2 levels are highly dependent on insulin (but not glucose) concentration, and the protein is under the control of the Adenosine 1 receptor. CNT family members are imperative in the response of cells to a variety of anticancer and antiviral nucleoside analogs, as the CNT proteins modulate their entry into target tissues. Increasing evidence also suggests that CNT2 may have a role in energy metabolism because activation of CNT2 relies on the opening of ATP-sensitive K+ channels.