“What we have done is prove that these cells do what working heart muscles do, which is beat in sync with the rest of the heart,” says Chuck Murry, a cardiovascular biologist at the University of Washington in Seattle, who co-led the research.
Cardiomyocytes derived from human embryonic stem (ES) cells typically beat fewer than 150 times a minute. External electrical stimulation can increase that rate, but only up to about 240 beats per minute, says Michael LaFlamme, a cardiovascular biologist at the University of Washington and the other co-leader on the project.
Rats and mice have heart rates of around 400 and 600 beats per minute, respectively. However, guinea pigs have a heart rate of 200–250 beats per minute, near the limit for human cardiomyocytes.
From the first experiment with the sensor in guinea pigs, it was obvious that the transplanted cells were beating in time with the rest of the heart, says LaFlamme. When he looked into the chest cavity, the heart “was flashing back at us”, he says.