The inositol 1,4,5-trisphosphate receptor channel in the endoplasmic reticulum is involved in neuronal transmission via Ca²⁺ signaling and for many other functions that relate to morphological and physiological processes in living organisms. We analysed the three-dimensional structure of the ligand-free form of the receptor based on single particle technique using an automatic particle picking system. We propose a model which explains the complex mechanism for the regulation of Ca²⁺ release by co-agonists, Ca²⁺, inositol 1,4,5-trisphosphate based on the structure of multiple internal cavities and a porous balloon-shaped cytoplasmic domain.

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