Autonomous regulation of free Ca 2+ concentrations in isolated plant cell nuclei: A mathematical analysis

membrane; NPC, nuclear pore complex; [Ca2+]nuc, nucleoplasmic free calcium concentration; [Ca2+]nuc_total, nucleoplasmic total calcium concentration; [Ca2+]store, nuclear store free calcium concentration; [Ca2+]store_total, nuclear store total calcium concentration. Experiments performed on nuclei isolated from animal or plant cells have provided evidence that the nucleus generates directly specific nucleoplasmic calcium transients in response to external stimuli. Recent data suggest that isolated plant nuclei might be considered as a closed system where the nuclear concentration of free calcium would be regulated by reversible movements between the nucleoplasm and nuclear stores. We have addressed the relevance of this hypothesis by developing a mathematical approach to simulate nucleoplasmic calcium dynamics generated under various pH and temperature conditions. Here, we show that the experimental results could be explained provided that calcium-channels as well as systems transporting calcium are present on the inner nuclear membrane. The putative channels would allow the entry of calcium into the nucleoplasm whereas the elusive transporting system(s) would contribute to replenish the nuclear stores. The simple proposed model is versatile enough to explain and predict autonomous changes in free calcium in the nucleoplasm of isolated plant nuclei. 1 1