Quantification of intracellular 'free' calcium in isolated coral cells of Stylophora pistillata in laboratory experiment

Despite its prominent role as an intracellular messenger in all organisms, intracellular free calcium ([Ca2+]i) has not been quantified in corals or cnidarians in general. Ratiometric calcium dyes and cell imaging have been key methods in successful research on [Ca2+]i in mammlian and plat model systems, and could be applied to corals. Here, we developed a procedure to quantity [Ca2+]i in isolated cells from the model coral species Stylophora pistillata using Indo-1 and confocal microscopy mainatined in aquarium culture at the Centre Scientifique de Monaco, Monaco between 2020 and 2023. We quantified [Ca2+]i in coral cells with and without intracellular dinoflagellate symbionts, and verified our procedure on cultured mammalian cells. We then used our procedure to measure changes in [Ca2+]i in coral cells exposed to the classic inhibitor of [Ca2+], thapsigargin, and also used it to record elevations in [Ca2+]i in coral cells undergoing apoptosis. Our procedure paves the way for future studies into intracellular calcium in corals and other cnidarians.