Extracellular ATP (eATP) induces an intracellular Ca2+ transient by activating phospholipase C (PLC)-associated P2X4 purinergic receptors, leading to production of inositol 1,4,5-trisphosphate (IP3) and subsequent Ca2+ release from intracellular stores in Mouse pancreatic beta-cells. Using laser scanning confocal microscopy, Ca2+ indicator fluo-4 AM, and the cell permeable nuclear indicator Hoechst 33342, we examined the properties of eATP-induced Ca2+ release in pancreatic P-cell nuclei. eATP induced a higher nuclear Ca2+ transient in pancreatic p-cell nuclei than in the cytosol. After pretreatment with thapsigargin (TG), an inhibitor of sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) pumps, the amplitude of eATP-induced Ca2+ transients in the nucleus was still much higher than those in the cytosol. This effect of eATP was not altered by inhibition of either the plasma membrane Ca2+-ATPase (PMCA) or the plasma membrane Na+/Ca2+ exchanger (NCX) by LaCl3 or by replacement of Na+ with N-Methyl-Glucosamine. eATP-induced nuclear Ca2+ transients were abolished by a cell-permeable IP3R inhibitor, 2-aminoethoxydiphenyl borate (2-APB), but were not blocked by the ryanodine receptor (RyR) antagonist ryanodine. Immunofluorescence studies showed that IP3Rs are expressed on the nuclear envelope of pancreatic beta-cells. These results indicate that eATP triggers nuclear Ca2+ transients by mobilizing a nuclear Ca2+ store via nuclear IP3Rs. (C) 2009 Elsevier Inc. All rights reserved.