PURPOSE: To provide a novel inositol triphosphate receptor which comprises a protein having a specific amino acid sequence, can bond to inositol triphosphate (IP3), thus is useful as a reagent for studying the action mechanism of IP3 and as a calcium release-inhibitor.

CONSTITUTION: This receptor comprises a protein which has an amino acid sequence including the amino acid sequence represented by the formula, can bond to IP3, thus is useful as a reagent for studying the action mechanism of IP3 and as a cardiotonicum (calcium release inhibitor). This protein is prepared by extracting mRNA from the cultured human cells of Burkitt lymphoma (Namalwa cells) in a usual manner, preparing the cDNA library therefrom, screening it using the antibody screening technique or a marked probe to select the clone containing the gene of type II IP3 and recovering the DNA, transducing it into a vector and expressing the gene in the host.