While the debate over the use of human embryonic stem cells for research purposes rages on in the U.S., researchers at the Technion-Israel Institute of Technology announced that they have successfully turned these famously versatile cells into the precursors of heart cells. Their results appear in the August issue of the Journal of Clinical Investigation.

The scientists started with a line of embryonic stem cells and first grew a mass of undifferentiated cells. They then moved the cells into a suspension containing growth factors designed to encourage differentiated growth. While dividing, the stem cells consolidated into so-called embryoid bodies, or microscopic clumps of cells. The researchers noticed that approximately 10 percent of these bodies contained cells that were spontaneously contractinga signature of cells called cardiomyocytes that develop into heart tissue in an embryo.

To test whether what they had created were in fact cardiomyocytes, the researchers ran a variety of tests. They analyzed the electrical and chemical activities of the cells, examined their structure with an electron microscope, investigated their responses to hormones such as adrenaline, and probed the genes and proteins within the cells. Comparing the results to known cardiomyocytes suggested that they had successfully cultured the cells.

Although co-author Lior Gepstein suggests it is likely these cells would produce mature human heart muscle cells once placed in an adult human heart, clinical applications are still a long way off. Because several million cells are needed to carry out heart repair, the research team's next goal is to produce pure cultures containing only cardiomyocytes.