Absence of equilibrative nucleoside transporter 1 in ENT1 knockout mice leads to altered nucleoside levels following hypoxic challenge

Abstract Aims Equilibrative nucleoside transporters (ENT) modulate the flux of adenosine. The ENT1-null (KO) mouse heart is endogenously cardioprotected but the cellular basis of this phenotype is unknown. Therefore, we investigated the cellular mechanisms underlying ENT1-mediated cardioprotection. Main methods Circulating adenosine levels were measured in WT and KO mice. Cellular levels of nucleosides and nucleotides were investigated in isolated adult cardiomyocytes from WT and KO mice using HPLC following hypoxic challenge (30 min, 2% O 2 ). Changes in hypoxic gene expression were analyzed by PCR arrays and cAMP levels were measured to investigate contributions from adenosine receptors. Key findings Circulating adenosine levels were significantly higher in KO (416 ± 42 nmol/l, n = 12) compared to WT animals (208 ± 21, n = 13, p  Significance ENT1 contributes to modulation of extracellular adenosine levels and subsequent purinergic signaling via ARs. ENT1-null mice possess elevated circulating adenosine levels and reduced cellular uptake resulting in a perpetually cardioprotected phenotype.