Induction of cardiac alternans in human iPS‐derived cardiomyocytes through β‐adrenergic receptor stimulation

Abstract

Abstract Cardiac alternans (C‐ALT) is a phenomenon of alternating strong and weak contractions in the heart and is considered a risk factor for the development of heart failure and arrhythmias. However, no model has been reported that can induce C‐ALT in vitro using human cells, and the developmental mechanism of C‐ALT has not been studied using human cells. In this study, we successfully induced C‐ALT in vitro using human‐induced pluripotent stem cell‐derived cardiomyocytes (hiPSC‐CMs). By stimulating β‐adrenergic receptor with isoproterenol on hiPSC‐CMs cultured in atmospheric condition (with ~0.04% CO2), contractility and calcium transient were observed to alternately increase and decrease with each beat. In contrast, C‐ALT was not induced in hiPSC‐CMs cultured at 5% CO2 concentration. Since previous studies have linked C‐ALT to problems with calcium regulation in the sarcoplasmic reticulum (SR), we exposed hiPSC‐CMs to compounds that alter SR Ca2+ loading and analyzed their contractile responses. The results showed that exposure to verapamil, thapsigargin, and ryanodine either suppressed or eliminated C‐ALT. In contrast, omecamtiv mecarbil and blebbistatin, which alter contractility without SR Ca2+ loading, did not induce or suppress C‐ALT. These results suggest that C‐ALT in hiPSC‐CMs induced by isoproterenol may be due to abnormal regulation of the ryanodine receptor's opening and closing caused by excessive Ca2+ load in the SR from β‐adrenergic receptor stimulation.

Keywords

• calcium alternans
• cardiac alternans
• cardiac contractility
• cell sheet technology
• human‐induced pluripotent stem cell‐derived cardiomyocytes