Optogenetic manipulation of Gq- and Gi/o-coupled receptor signaling in neurons and heart muscle cells

G protein-coupled receptors (GPCRs) transmit extracellular signals into the cell depending on the type of G protein. To analyze the functions of GPCR signaling, we developed optogenetic tools using animal G protein-coupled bistable rhodopsins that can be controlled into active and inactive states by light irradiation. We expressed Gq- and Gi/o-coupled bistable rhodopsins in hindbrain reticulospinal V2a neurons, which are involved in locomotion, or in cardiomyocytes of zebrafish. Light stimulation of the reticulospinal V2a neurons expressing Gq-coupled spider Rh1 resulted in an increase in the level of cytoplasmic Ca ²⁺ and evoked swimming behavior. Light stimulation of cardiomyocytes expressing the Gi/o-coupled mosquito Opn3, pufferfish TMT opsin, or lamprey parapinopsin induced cardiac arrest, and the effect was suppressed by treatment with pertussis toxin or barium, suggesting that Gi/o-dependent regulation of inward-rectifier K ⁺ channels controls cardiac function. These data indicate that these rhodopsins are useful for optogenetic control of GPCR-mediated signaling in neurons and cardiomyocytes in vivo .