Abstract
We have identified three distinct groups of mitochondria in normal living pancreatic acinar cells, located (i) in the peripheral basolateral region close to the plasma membrane, (ii) around the nucleus and (iii) in the periphery of the granular region separating the granules from the basolateral area. Three-dimensional reconstruction of confocal slices showed that the perigranular mitochondria form a barrier surrounding the whole of the granular region. Cytosolic Ca(2+) oscillations initiated in the granular area triggered mitochondrial Ca(2+) uptake mainly in the perigranular area. The most intensive uptake occurred in the mitochondria close to the apical plasma membrane. Store-operated Ca(2+) influx through the basolateral membrane caused preferential Ca(2+) uptake into sub-plasmalemmal mitochondria. The perinuclear mitochondria were activated specifically by local uncaging of Ca(2+) in the nucleus. These mitochondria could isolate nuclear and cytosolic Ca(2+) signalling. Photobleaching experiments indicated that different groups of mitochondria were not luminally connected. The three mitochondrial groups are activated independently by specific spatiotemporal patterns of cytosolic Ca(2+) signals and can therefore participate in the local regulation of Ca(2+) homeostasis and energy supply.
Highlights
Much recent Ca2+ signalling work has dealt with the importance of the mitochondria
There was heavy staining with ERtracker in the basolateral areas surrounding the granular region, except in the nucleus (n = 6)
High resolution confocal images of NADH autouorescence showed the locations of the mitochondria, which were predominantly grouped in a central perigranular area and in a peripheral area close to the plasma membrane (n = 26)
Summary
Much recent Ca2+ signalling work has dealt with the importance of the mitochondria. Contrary to conclusions from earlier work, it is clear that mitochondria can and do take up Ca2+ during normal Ca2+ signalling events and release it much more slowly (Pozzan et al, 1994, 2000; Duchen, 2000; Rutter and Rizzuto, 2000). Ca2+ in the mitochondria is of importance for the regulation of metabolism, since three dehydrogenases of the Krebs cycle are modulated by the Ca2+ concentration in the micromolar range (Denton and McCormack, 1990; McCormack et al, 1990). Repetitive cytosolic Ca2+ spikes ã European Molecular Biology Organization induce mitochondrial Ca2+ spikes. Agonist stimulation, evoking cytosolic and mitochondrial Ca2+
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