Introduction: Human induced pluripotent stem cell (hiPSC) represent an attractive source of cardiomyocytes (CMs) in cardiovascular research. Also, the beating rate and the response of the β-ARs (β-adrenoceptors) represent valuable parameters for drug screening, regenerative medicine, and disease modeling. 

Methods and Results: Our results showed that mRNA expression of the β₁-AR was significantly up-regulated (10.19±6.29, p<0.04) in 28 days old CMs in comparison to early-stage CM and undifferentiated hiPSC. Further, we found that hiPSC-derived CM responded to β-adrenergic drugs and showed a significant increase in beating frequency after 3 hours (70.3±10.2 to 165.3±12.7 beats/min, p<0.001) following epinephrine treatment. Interestingly, the effect of epinephrine was abolished in CMs co-incubated with propranolol, which was also accompanied by a significant reduction in overall beating frequency (44±5.49 beats/min, p<0.001). An evaluation of the [Ca²⁺]_i oscillation in 28 days old CMs revealed a significant increase in [Ca²⁺]_i oscillation (1.0±0.10 versus 1.6±0.13, p<0.01) in epinephrine (50 µM) and (1.0±0.13 versus 1.43±0.15, p<0.05) in dobutamine (200 µM). In addition, in CMs treated with propranolol (non-selective antagonist β-AR) and atenolol (selective antagonist β₁-AR), a significant reduction in [Ca²⁺]_i oscillation (1.0±0.11 versus 0.59±0.17, p<0.05) and (1.0±0.15 versus 0.7±0.12, p<0.05), respectively, was found. Furthermore, higher doses of propranolol and atenolol at 50 µM and 120 µM, respectively, completely inhibited the [Ca²⁺]_i transients. Interestingly, the inhibitory effect of atenolol (120 µM) could be restored by the β₁-AR agonist dobutamine (200 µM), suggesting a physiological coupling of negative and positive effects mediated by the β₁-adrenergic system.