The adenosine transporter, ENT1, in cardiomyocytes is sensitive to inhibition by ethanol in a kinase-dependent manner: implications for ethanol-dependent cardioprotection and nucleoside analog drug cytotoxicity

The adenosine transporter 1 (ENT1) transports nucleosides, such as adenosine, and cytotoxic nucleoside analog drugs. ENT1 is well established to play a role in adenosinergic signaling in the cardiovascular system by modulating adenosine levels. Moderate ethanol consumption is cardioprotective and underlying mechanisms of action are not clear although adenosinergic signaling has been implicated. Here, we show that ethanol (5-200 mM) significantly reduces ENT1-dependent [H-3] 2-chloroadenosine uptake (by up to 27 %) in the cardiomyocyte cell line, HL-1. Inhibition or absence of ENT1 is known to be cardioprotective, suggesting that the interaction of ethanol with ENT1 may promote adenosinergic cardioprotective pathways in the cardiovasculature. Ethanol sensitivity of adenosine uptake is altered by pharmacological activation of PKA and PKC. Primary cardiomyocytes from PKC epsilon-null mice have significantly greater sensitivity to inhibition (by approximately 37 %) of adenosine uptake by ethanol than controls. These data suggest that the presence of ethanol may compromise ENT1-dependent nucleoside analog drug cytotoxicity, and indeed, ethanol (5 mM) reduces the cytotoxic effects of gemcitabine (2 nM), an anti-cancer drug, in the human cancer cell line, HTB2. Thus, the pharmacological inhibition of ENT1 by ethanol may contribute to ethanol-dependent cardioprotection but compromise gemcitabine cytotoxicity.