Calcium signalling in and around the nuclear envelope

We have compared calcium mobilization by Ins(1,4,5)P₃(IP₃), cADP-ribose (cADPR) and nicotinic acid–adenosine dinucleotide phosphate (NAADP) from the envelope of isolated nuclei with the calcium signalling in intact isolated pancreatic acinar cells. Ca²⁺ uptake and release were studied with calcium-sensitive fluorescent probes. In the present study, we have shown that all calcium messengers induce Ca²⁺ release from the nuclear envelope. Pre-treatment of nuclei with thapsigargin completely abolished the responses to the calcium messengers, indicating that Ca²⁺ stores in isolated nuclei are thapsigargin-sensitive. Using different pharmacological tools, we show that Ca²⁺ release from pancreatic nuclei is unlikely to occur from stores other than those with endoplasmic reticulum characteristics. We conclude that all three calcium messengers can release Ca²⁺ from pancreatic acinar nuclear stores, as previously shown for IP₃ and cADPR. It would appear that NAADP releases Ca²⁺ from the same IP₃- and cADPR-sensitive stores with endoplasmic reticulum characteristics.