Nucleoside transporter expression profiles in human cardiac tissue show striking individual variability with overall predominance of hENT1

Nucleoside transporters (NTs) are integral membrane transport proteins that modulate the flux of nucleosides such as adenosine across cell membranes. Two families of NTs exist, the concentrative NTs (CNTs, SLC28) and the equilibrative NTs (ENTs, SLC29). CNTs and ENTs transport anti-cancer and anti-viral nucleoside analog drugs and ENTs are also targets of drugs used to treat cardiac pathologies. Levels of some NT profiles have been shown to relate to clinical outcomes in the use of nucleoside analog drugs. However, currently, patient NT profile is not assessed prior to pharmacological administration of analog drugs. Here we describe a reliable method to determine a complete individual NT expression profile from human tissue using quantitative real-time PCR. We developed this assay on tissue (right atrial appendage, left internal mammary, aorta) from individuals undergoing cardiac surgery and compared these findings to the NT expression profiles in pooled whole heart tissue (normal and diseased). Data show that hENT1 is the most abundantly expressed NT, with highest expression levels in the aorta. However, NT expression profiles are highly variable among individuals and changes in NT expression between normal and diseased tissues were observed. These data are the first to describe the RNA expression patterns of all seven NT isoforms in the human heart. The methodology described here may be useful for quantitatively characterizing complete NT expression profiles in any human target tissue.