Optogenetic manipulation of second messengers in neurons and cardiomyocytes with microbial rhodopsins and adenylyl cyclase

Even though microbial photosensitive proteins have been used for optogenetics, their use should be optimized to precisely control second messengers in vivo . We exploited Gt CCR4 and Kn ChR, cation channelrhodopsins from algae, Be GC1, a guanylyl cyclase rhodopsin from a fungus, and photoactivated adenylyl cyclases (PACs) from cyanobacteria ( Oa PAC) or bacteria ( b PAC), to control cell functions in zebrafish. Optical activation of Gt CCR4 and Kn ChR in the hindbrain reticulospinal V2a neurons, which are involved in locomotion, immediately induced swimming behavior, whereas activation of Be GC1 or PACs was achieved at a short latency. Kn ChR had the highest locomotion-inducing activity of all the channelrhodopsins examined. Activation of Gt CCR4 and Kn ChR in cardiomyocytes induced cardiac arrest, whereas activation of b PAC gradually induced bradycardia. Kn ChR activation led to an increase in intracellular Ca2+ in the heart, suggesting that depolarization caused cardiac arrest. These data suggest that these optogenetic tools can be used to reveal the roles of second messengers in various cell types in vertebrates. ### Competing Interest Statement The authors have declared no competing interest.