Presence of the inositol 1,4,5-triphosphate receptor isoforms in the nucleoplasm

Although the inositol 1,4,5-triphosphate (IP3)-induced nuclear Ca2+ release has been shown to play key roles in nuclear functions, the presence of IP3 receptor (IP3R)/Ca2+ channels in the nucleoplasm has not been found. Recently, the IP3R/Ca2+ channels were reported to exist in the nucleoplasmic reticulum structure, an extension of the nuclear envelope. Here we investigated the potential existence of the IP(3)Rs in the nucleoplasm and found the presence of all three IP3R isoforms in neuroendocrine and non-neuroendocrine cells. The IP(3)Rs were widely scattered in the nucleoplasm, localizing in both the heterochromatin and euchromatin regions. (C) 2003 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.