Figure 4. Sympathetic neurons promote cardiomyocyte proliferation via β‐adrenergic signalling .

A, when β‐adrenergic signalling was blocked in co‐cultures with propranolol (2 μm) during the entire 5 day culture period there was a decrease in cardiomyocyte proliferation, as measured by the number of PH3+ cardiomyocytes. There was no significant effect of treatment with the β‐adrenergic agonist isoproterenol (10 μm) in myocyte‐only cultures, although proliferation was decreased compared to co‐culture conditions (n = 5). B, β₁ and β₂ signalling was blocked in 5 day co‐cultures with bisoprolol (left) and ICI‐118,551 (right), respectively. When β₂‐adrenergic receptors were blocked with ICI‐118,551, there was a significant decrease in cardiomyocyte proliferation (n = 3). C, when cholinergic signalling was blocked with the cholinergic antagonist scopolamine (10 μm) in co‐cultures, we could not detect an effect on the number of PH3+ cells. Stimulating cholinergic signalling in myocyte‐only cultures with the cholinergic agonist muscarine (2.5 μm) also had no effect. (n = 3; *P < 0.05 vs. co‐culture.)