Optical control of beating behavior in cardiomyocytes using photoactivated adenylyl cyclase

Photoactivated adenylyl cyclase (PAC) is a photoreceptor protein derived from microorganisms that enables intracellular production of cyclic adenosine monophosphate (cAMP) upon blue light illumination. In this study, we expressed a bacterial PAC in human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and investigated whether their beating behavior could be modulated by light. Using a calcium-specific fluorescent probe to monitor myocardial contractions, we observed an increase in the frequency of Ca²⁺ transients 20 seconds after light illumination, which returned to baseline within 5 minutes. In contrast, treatment with 10μM forskolin—a known activator of endogenous adenylyl cyclase—also increased the beating rate, but the effect persisted for 40 minutes and did not return to baseline until 4 hours after washing. The light-induced change in beating behavior in hiPSC-CMs is precisely controllable, highly reversible, and dependent on photon flux density. Moreover, increasing the illumination intensity beyond a certain threshold temporarily halted the beating, which resumed after a few minutes. These findings suggest that PAC-mediated light stimulation can be used to precisely control myocardial beating and replicate abnormal cardiac conditions. Notably, analysis of single PAC-expressing cardiomyocytes revealed that blue light activation enhanced the amplitude of cell size changes during contraction and relaxation, indicating that not only heart rate but also contractile force was modulated. PAC, which allows direct control of second messenger signaling in cardiomyocytes, holds promise as a versatile tool for drug screening, toxicity assessment, and optical pacing applications.