Modulation of [Ca2+] Signaling Dynamics and Metabolism by Perinuclear Mitochondria in Mouse Parotid Acinar Cells

Abstract

[Ca 2ϩ ] i signals may be tuned to evoke specific physiological responses in these cells. The major function of pancreatic acinar cells is the exocytosis of zymogen granules that can be activated by apically confined [Ca 2ϩ ] i signals (6), suggested to be the major physiological [Ca 2ϩ ] i signal evoked by threshold agonist concentrations (7). These apically confined [Ca 2ϩ ] i signals are in part because of the distribution of mitochondria, which form a belt around the apically located zymogen granules (8, 9). These perigranular mitochondria likely serve two main functions. First, mitochondrial Ca 2ϩ uptake provides a buffer barrier thereby preventing the spread of [Ca 2ϩ ] i waves to the basal part of the cell (8 -10). Second, the Ca 2ϩ taken up by mitochondria drives ATP production locally for the energy-consuming exocytotic process (11). The major function of parotid acinar cells is fluid secretion, and this is most effectively activated by rapid global [Ca 2ϩ ] i signals. We proposed that rapid global [Ca 2ϩ ] i signals facilitate the almost simultaneous activation of Ca 2ϩ -dependent Cl Ϫ channels on the apical membrane and Ca 2ϩ -dependent K ϩ channels on the basolateral membrane (5). The latter maintain the membrane potential at hyperpolarizing potentials and the driving force for Cl Ϫ efflux, thereby ensuring efficient ion and water movement (12). Interestingly, even at threshold stimulation parotid acinar cells exhibit rapid global [Ca 2ϩ ] i signals, and apically confined [Ca 2ϩ ] i signals were never observed (5). Given the many similarities between parotid and pancreatic acinar cells, the differences in the spatial and temporal patterns of [Ca 2ϩ ] i signaling between these two cell types 1 The abbreviations used are: [Ca 2ϩ ] i , intracellular calcium concentration; CCh, carbamylcholine (carbachol); FCCP, carbonyl cyanide 4-trifluoro-methoxyphenylhydrazone; OGB2, Oregon Green BAPTA 2; InsP 3 , inositol 1,4,5-trisphosphate; caged InsP 3 , D-myo-InsP 3 P-4(5)-1-(2-nitrophenyl)-ethyl ester; CaM, calmodulin; RuRed, ruthenium red; NPC, nuclear pore complex; rhod, rhodamine; TRITC, tetramethylrhodamine isothiocyanate.

Amplitude modulation of nuclear Ca2+ signals in human skeletal myotubes: A possible role for nuclear Ca2+ buffering

“…Moreover, the onset of the increase in [Ca 2+ ] N did not differ from that in [Ca 2+ ] S within the sampling interval of our recordings (33 ms). In contrast to our study, a significant delay (∼300 ms) was observed in carbachol-stimulated parotid acinar cells [33]. In these cells, the majority of mitochondria are localized around the nucleus and it was found that inhibitors of mitochondrial Ca 2+ uptake abolished this delay suggesting the involvement of these organelles in propagation of the Ca 2+ signal from the cytosol into the nucleus.…”

“…Because strategically localized mitochondria have dramatic effects on the propagation of intracellular Ca 2+ signals [32,33], we determined their subcellular localization by expressing a mitochondria-targeted variant of yellow fluorescent protein (COX8-EYFP) using a transfection method described previously [34]. Fig.…”

Dynamics of mitochondrial [Ca2+] measured with the low-Ca2+-affinity dye rhod-5N

“…However, the discrepancy in the size of the initial [Ca 2+ ] M peak may also be due to the high affinity of the dye. In fact, the lower affinity dye rhod-FF (Kd = 19 M) has been used in some cases to avoid saturation with Ca 2+ or to minimize the signal coming from mistargeted cytosolic dye [17,18]. In these papers, although the data were not calibrated in [Ca 2+ ] values, it was actually shown that rhod-2 saturated with Ca 2+ in mitochondria during cell stimulation, while rhod-FF had a better response.…”

Mitochondria in stem cells

“…Numerous types of differentiated cells have also been reported to exhibit perinuclear arrangements of mitochondria, including fibroblasts (Yaffe, 1999), pancreatic ascinar cells (Johnson et al, 2003;Bruce et al, 2004), and astrocytes and neurons (Collins et al, 2002). The addition of ES and adult stem cells to this list reopens the question "Is there a benefit for some cells having a perinuclear arrangement of mitochondria in comparison to cell types that do not?"…”