This study investigates the properties of OLPVR1, a viral rhodopsin found in the genome of giant viruses infecting phytoplankton, and two other type 1 viral channelrhodopsins (VCR1s). The research demonstrates that VCR1s accumulate intracellularly and, upon illumination, induce calcium release from intracellular IP₃-dependent stores. In vivo, this light-induced calcium release is sufficient to remotely control muscle contraction in VCR1-expressing tadpoles. The ability of VCR1s to photorelease calcium without altering plasma membrane electrical properties suggests they could be potential precursors for optogenetic tools, with applications in basic research and medicine. Rhodopsins are light-driven membrane proteins found in many organisms, including bacteria and humans. They are known for their ability to transport ions, either as proton pumps like bacteriorhodopsins or as ion channels like channelrhodopsins. When expressed in the plasma membrane of mammalian cells, channelrhodopsins can modify cell excitability with high spatiotemporal resolution upon illumination, a property that underpins optogenetics. The study shows that OLPVR1, a viral rhodopsin, is expressed intracellularly in Xenopus oocytes and triggers an increase in cytoplasmic calcium proportional to the light power applied. This function is unique among rhodopsins and suggests that VCR1s could be used in a variety of cells where a direct link between intracellular calcium and cell function exists. The study also shows that light irradiation reversibly modifies tail movements of OLPVR1-expressing frog tadpoles. The research further demonstrates that OLPVR1 expression produces light-activated currents with features similar to endogenous CaCCs of oocytes. These currents require intracellular calcium, and the study shows that OLPVR1 can induce calcium release from intracellular stores, similar to IP₃ receptors. The study also shows that OLPVR1 can activate surface CaCCs through release of intracellular calcium, and that this process is distinct from the mechanisms of ChR2. The study also shows that OLPVR1 localizes to the ER and activates surface Ca²⁺-activated channels through release of intracellular Ca²⁺. The study further shows that OLPVR1 can activate a fluorescence Ca²⁺ sensor in its immediate vicinity even in the presence of the fast Ca²⁺ chelator BAPTA-AM. The study also shows that OLPVR1 can induce light-driven muscle contraction in Xenopus tadpoles, suggesting that OLPVR1 can be expressed in living animals and produce light-dependent behavioural changes. The study concludes that VCR1s have the potential to be used as optogenetic tools, with potential applications in basic research and medicine. The study also suggests that hijacking intracellular Ca²⁺ dynamics is a strategy used byThis study investigates the properties of OLPVR1, a viral rhodopsin found in the genome of giant viruses infecting phytoplankton, and two other type 1 viral channelrhodopsins (VCR1s). The research demonstrates that VCR1s accumulate intracellularly and, upon illumination, induce calcium release from intracellular IP₃-dependent stores. In vivo, this light-induced calcium release is sufficient to remotely control muscle contraction in VCR1-expressing tadpoles. The ability of VCR1s to photorelease calcium without altering plasma membrane electrical properties suggests they could be potential precursors for optogenetic tools, with applications in basic research and medicine. Rhodopsins are light-driven membrane proteins found in many organisms, including bacteria and humans. They are known for their ability to transport ions, either as proton pumps like bacteriorhodopsins or as ion channels like channelrhodopsins. When expressed in the plasma membrane of mammalian cells, channelrhodopsins can modify cell excitability with high spatiotemporal resolution upon illumination, a property that underpins optogenetics. The study shows that OLPVR1, a viral rhodopsin, is expressed intracellularly in Xenopus oocytes and triggers an increase in cytoplasmic calcium proportional to the light power applied. This function is unique among rhodopsins and suggests that VCR1s could be used in a variety of cells where a direct link between intracellular calcium and cell function exists. The study also shows that light irradiation reversibly modifies tail movements of OLPVR1-expressing frog tadpoles. The research further demonstrates that OLPVR1 expression produces light-activated currents with features similar to endogenous CaCCs of oocytes. These currents require intracellular calcium, and the study shows that OLPVR1 can induce calcium release from intracellular stores, similar to IP₃ receptors. The study also shows that OLPVR1 can activate surface CaCCs through release of intracellular calcium, and that this process is distinct from the mechanisms of ChR2. The study also shows that OLPVR1 localizes to the ER and activates surface Ca²⁺-activated channels through release of intracellular Ca²⁺. The study further shows that OLPVR1 can activate a fluorescence Ca²⁺ sensor in its immediate vicinity even in the presence of the fast Ca²⁺ chelator BAPTA-AM. The study also shows that OLPVR1 can induce light-driven muscle contraction in Xenopus tadpoles, suggesting that OLPVR1 can be expressed in living animals and produce light-dependent behavioural changes. The study concludes that VCR1s have the potential to be used as optogenetic tools, with potential applications in basic research and medicine. The study also suggests that hijacking intracellular Ca²⁺ dynamics is a strategy used by