Investigating the InsP₃ Receptor in Living Cells by Caged InsP₃

The inositol 1,4,5-trisphosphate receptor (InsP₃R) operates as an intracellular ligand-gated Ca²⁺ channel and plays a pivotal role in cellular Ca²⁺ homeostasis across all living cells. It is activated following membrane receptor-ligand interactions and stimulation of subsequent signaling cascades involving the enzymatic breakdown of the membrane lipid phosphatidyl-4,5-bisphosphate (PIP₂) into the membrane-delimited second messenger diacylglycerol (DAG) and the diffusible second messenger inositol-1,4,5-trisphophate (InsP₃). Modulation of InsP₃R's activity is thus involved in a plethora of physiological and pathological processes. Here we combine membrane permeable photoactive caged-InsP₃ with Ca²⁺ imaging techniques in living cells to study the channel's in vivo properties. Using UV-flashes of variable energy, the activity properties of InsP₃R can be investigated in great detail in its native environment.