Measurement of Inositol(1,4,5)Trisphosphate Using a Stereospecific Radioreceptor Mass Assay

Inositol(1,4,5)trisphosphate [Ins(1,4,5)P₃ ] is an important second messenger that activates its cognate Ins(1,4,5)P₃ receptor to release Ca²⁺ from intracellular stores. The assay described in this chapter uses the Ins(1,4,5)P₃ receptor (essentially as a binding protein) to measure the biologically active trisphosphate (specifically from other trisphosphates). The binding protein (Ins(1,4,5)P3 receptor) is prepared from Bovine adrenal glands and this is mixed with [³ H]-labeled and unlabeled (generated from biological samples or standards) Ins(1,4,5)P₃ . Using the same principles as for radioimmunoassay/ELISA the mass of Ins(1,4,5)P₃ in biological samples can be estimated.