Association pattern of the heterooligomer of inositol 1, 4, 5-trisphosphate receptors

Functional IP3-sensitive intracellular Ca2- release channel is considered to be a tetramer of IP3R. Heterooligomeric complexes composed of distinct types of IP3R have been reported, however, evidences for them being tetramer have not appeared. Here we report that heterooligomer composed of IP(3)R1 and IP(3)R2 also exists as tetramer. The heterooligomer was immunoprecipitated with IP(3)R1-specific antibody and detected by Western blot analysis with IP(3)R2-specific antibody. Tetramer, trimer, dimer and monomer were detected. The immunoprecipitating antibody (IP(3)R1-specific) does not crossreact with IP(3)R2, and tetramer was the major native product of the TP,R complex containing IP(3)R2 as part(s). Thus we conclude tetramer is the native form of heterooligomer composed of IP(3)R1 and IP(3)R2.