Figure 7. β‐Adrenergic signalling undergoes a developmental shift from a negative to a positive regulator of cardiomyocyte hypertrophy .

A, bar plot comparing the average cell size of 3‐week‐old cardiomyocytes cultured without (left) or with (right) sympathetic neurons. Cultures were either treated with isoproterenol (10 μm; grey) for the last 4 days in vitro or not treated (black). Four days of isoproterenol treatment was sufficient to induce an increase in cardiomyocyte size. B, a plot of average cardiomyocyte size over days in vitro shows that, at 4 and 8 DIV, treatment with isoproterenol (grey line) decreases cardiomyocyte size, compared to the control. As the cardiomyocytes mature in culture, the effect of isoproterenol reverses, with a significant increase in cardiomyocyte size seen at 24 DIV. For each time point, cultures were treated with isoproterenol for the last 4 days of the culture period. (n = 3; *P < 0.05 vs. age‐matched control.)