Monitoring Calcium Dynamics in Pig Intestinal Organoids with FLIM and FRET

Intracellular calcium signaling plays a crucial role in intestinal epithelial function. In this chapter, we describe a method to monitor calcium dynamics in live pig small intestinal organoids using stably expressed genetically encoded FRET-based biosensor in combination with intensity-based ratiometric and fluorescence lifetime imaging (FLIM) microscopy readouts. The calcium biosensor Twitch-2B was introduced into organoids by electroporation. Despite the modest lifetime contrast, the biosensor provides a highly reliable ratiometric signal and is compatible with both conventional fluorescence and FLIM-based imaging platform. Following electroporation, organoids are allowed to form and subsequently were selected to establish stable biosensor-expressing lines. This is followed by the live microscopy of heterogeneous and cell-specific calcium responses upon pharmacological stimulation. The presented protocol offers a versatile approach for studies of calcium signaling in relevant 3D cell models, such as organoids and tissues-on-a-chip.