Human C-kit+CD45− cardiac stem cells are heterogeneous and display both cardiac and endothelial commitment by single-cell qPCR analysis

•Human right and left atrial biopsies were analysed for C-kit and CD45 expression.•The C-kit+CD45− progenitor population was predominantly confined to right atrium.•Heterogeneity within this population was determined by single-cell qPCR.•Most of the C-kit+CD45− cells expressed endothelial genes.•Some cells negative for endothelial genes, showed signs of cardiac commitment. C-kit expressing cardiac stem cells have been described as multipotent. We have previously identified human cardiac C-kit+CD45− cells, but only found evidence of endothelial commitment. A small cardiac committed subpopulation within the C-kit+CD45− population might however be present. To investigate this at single-cell level, right and left atrial biopsies were dissociated and analyzed by FACS. Only right atrial biopsies contained a clearly distinguishable C-kit+CD45− population, which was single-cell sorted for qPCR. A minor portion of the sorted cells (1.1%) expressed early cardiac gene NKX2.5 while most of the cells (81%) expressed late endothelial gene VWF. VWF− cells were analyzed for a wider panel of genes. One group of these cells expressed endothelial genes (FLK-1, CD31) while another group expressed late cardiac genes (TNNT2, ACTC1). In conclusion, human C-kit+CD45− cells were predominantly localized to the right atrium. While most of these cells expressed endothelial genes, a minor portion expressed cardiac genes.