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

Although the inositol 1,4,5-triphosphate (IP(3))-induced nuclear Ca(2+) release has been shown to play key roles in nuclear functions, the presence of IP(3) receptor (IP(3)R)/Ca(2+) channels in the nucleoplasm has not been found. Recently, the IP(3)R/Ca(2+) 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 IP(3)R 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.