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1.
The mechanisms and regulation of mitochondrial Ca2+ transport 总被引:4,自引:0,他引:4
2.
Leung YM Ahmed I Sheu L Tsushima RG Diamant NE Gaisano HY 《Biochemical and biophysical research communications》2006,345(1):340-344
In low or absence of glucose, alpha-cells generate rhythmic action potentials and secrete glucagon. alpha-Cell T-type Ca(2+) channels are believed to be pacemaker channels, which are expected to open near the resting membrane potential (around -60 mV) to initiate a small depolarization. A previous publication, however, showed that alpha-cell T-type Ca(2+) channels have an activation threshold of -40 mV, which does not appear to fulfill their role as pacemakers. In this work, we investigated the Ca(2+) channel characteristics in alpha-cells of mouse-insulin-promoter green-fluorescent-protein (MIP-GFP) mouse. The beta-cells of MIP-GFP were conveniently distinguished as green cells, while immunostaining indicated that the majority of non-green cells were alpha-cells. We found that majority of alpha-cells possessed T-type Ca(2+) channels having an activation threshold of -40 mV; these cells also had high-voltage-activated (HVA) Ca(2+) channels (activation threshold of -20 mV). A novel finding here is that a minority of alpha-cells had T-type Ca(2+) channels with an activation threshold of -60 mV. This minor population of alpha-cells was, surprisingly, devoid of HVA Ca(2+) channels. We suggest that this alpha-cell subpopulation may act as pacemaker cells in low or absence of glucose. 相似文献
3.
We investigated the effect of cytosolic and extracellular Ca2+ on Ca2+ signals in pancreatic acinar cells by measuring Ca2+ concentration in the cytosol([Ca2+]c) and in the lumen of the ER([Ca2+]Lu). To control buffers and dye in the cytosol, a patch-clamp microelectrode was employed. Acetylcholine released Ca2+ mainly from the basolateral ER-rich part of the cell. The rate of Ca2+ release from the ER was highly sensitive to the buffering of [Ca2+]c whereas ER Ca2+ refilling was enhanced by supplying free Ca2+ to the cytosol with [Ca2+]c clamped at resting levels with a patch pipette containing 10 mM BAPTA and 2 mM Ca2+. Elevation of extracellular Ca2+ to 10 mM from 1 mM raised resting [Ca2+]c slightly and often generated [Ca2+]c oscillations in single or clustered cells. Although pancreatic acinar cells are reported to have extracellular Ca2+-sensing receptors linked to phospholipase C that mobilize Ca2+ from the ER, exposure of cells to 10 mM Ca2+ did not decrease [Ca2+]Lu but rather raised it. From these findings we conclude that 1) ER Ca2+ release is strictly regulated by feedback inhibition of [Ca2+]c, 2) ER Ca2+ refilling is determined by the rate of Ca2+ influx and occurs mainly in the tiny subplasmalemmal spaces, 3) extracellular Ca2+-induced [Ca2+]c oscillations appear to be triggered not by activation of extracellular Ca2+-sensing receptors but by the ER sensitised by elevated [Ca2+]c and [Ca2+]Lu. 相似文献
4.
Tudurí E Filiputti E Carneiro EM Quesada I 《American journal of physiology. Endocrinology and metabolism》2008,294(5):E952-E960
Glucagon secreted from pancreatic alpha-cells plays a critical role in glycemia, mainly by hepatic glucose mobilization. In diabetic patients, an impaired control of glucagon release can worsen glucose homeostasis. Despite its importance, the mechanisms that regulate its secretion are still poorly understood. Since alpha-cells are particularly sensitive to neural and paracrine factors, in this report we studied the role of purinergic receptors and extracellular ATP, which can be released from nerve terminals and beta-cell secretory granules. Using immunocytochemistry, we identified in alpha-cells the P2 receptor subtype P2Y1, as well as the P1 receptors A1 and A2A. In contrast, only P2Y1 and A1 receptors were localized in beta-cells. To analyze the role of purinergic receptors in alpha-cell function, we studied their participation in Ca2+ signaling. At low glucose concentrations, mouse alpha-cells exhibited the characteristic oscillatory Ca2+ signals that lead to secretion. Application of ATP (1-10 microM) abolished these oscillations or reduced their frequency in alpha-cells within intact islets and isolated in culture. ATPgammaS, a nonhydrolyzable ATP derivative, indicated that the ATP effect was mainly direct rather than through ATP-hydrolytic products. Additionally, adenosine (1-10 microM) was also found to reduce Ca2+ signals. ATP-mediated inhibition of Ca2+ signaling was accompanied by a decrease in glucagon release from intact islets in contrast to the adenosine effect. Using pharmacological agonists, we found that only P2Y1 and A2A were likely involved in the inhibitory effect on Ca2+ signaling. All these findings indicate that extracellular ATP and purinergic stimulation are effective regulators of the alpha-cell function. 相似文献
5.
6.
Summary The intracellular pH (pH
i
) of Ehrlich ascites tumor cells, both in the steady state and under conditions of acid loading or recovery from acid loading, was investigated by measuring the transmembrane flux of H+ equivalents and correlating this with changes in the distribution ratio of dimethyloxazolidine-2,4-dione (DMO). The pH
i
of cells placed in an acidic medium (pH
o
below 7.15) decreases and reaches a steady-state value that is more alkaline than the outside. For example when pH
o
is acutely reduced to 5.5, pH
i
falls exponentially from 7.20 ± 0.06 to 6.29 ± 0.04 with a halftime of 5.92 ± 1.37 min, suggesting a rapid influx of H+. The unidirectional influx of H+ exhibits saturation kinetics with respect to extracellular [H+]; the maximal flux is 15.8 ± 0.05 mmol/(kg dry wt · min) andK
m
is 0.74 ± 0.09 × 10–6
m.Steady-state cells with pH
i
above 6.8 continuously extrude H+ by a process that is not dependent on ATP but is inhibited by anaerobiosis. Acid-loaded cells (pH
i
6.3) when returned to pH
o
7.3 medium respond by transporting H+, resulting in a rapid rise in pH
i
. The halftime for this process is 1.09 ± 0.22 min. The H+ efflux measured under similar conditions increases as the intracellular acid load increases. An ATP-independent as well as an ATP-dependent efflux contributes to the restoration of pH
i
to its steady-state value. 相似文献
7.
Support from the National Institutes of Health and the American Heart Association is gratefully acknowledged. 相似文献
8.
Liu J Kohler JE Blass AL Moncaster JA Mocofanescu A Marcus MA Blakely EA Bjornstad KA Amarasiriwardena C Casey N Goldstein LE Soybel DI 《PloS one》2011,6(6):e19638
Background and Aims
Recent work has suggested that Zn2+ plays a critical role in regulating acidity within the secretory compartments of isolated gastric glands. Here, we investigate the content, distribution and demand for Zn2+ in gastric mucosa under baseline conditions and its regulation during secretory stimulation.Methods and Findings
Content and distribution of zinc were evaluated in sections of whole gastric mucosa using X-ray fluorescence microscopy. Significant stores of Zn2+ were identified in neural elements of the muscularis, glandular areas enriched in parietal cells, and apical regions of the surface epithelium. In in vivo studies, extraction of the low abundance isotope, 70Zn2+, from the circulation was demonstrated in samples of mucosal tissue 24 hours or 72 hours after infusion (250 µg/kg). In in vitro studies, uptake of 70Zn2+ from media was demonstrated in isolated rabbit gastric glands following exposure to concentrations as low as 10 nM. In additional studies, demand of individual gastric parietal cells for Zn2+ was monitored using the fluorescent zinc reporter, fluozin-3, by measuring increases in free intracellular concentrations of Zn2+ {[Zn2+]i} during exposure to standard extracellular concentrations of Zn2+ (10 µM) for standard intervals of time. Under resting conditions, demand for extracellular Zn2+ increased with exposure to secretagogues (forskolin, carbachol/histamine) and under conditions associated with increased intracellular Ca2+ {[Ca2+]i}. Uptake of Zn2+ was abolished following removal of extracellular Ca2+ or depletion of intracellular Ca2+ stores, suggesting that demand for extracellular Zn2+ increases and depends on influx of extracellular Ca2+.Conclusions
This study is the first to characterize the content and distribution of Zn2+ in an organ of the gastrointestinal tract. Our findings offer the novel interpretation, that Ca2+ integrates basolateral demand for Zn2+ with stimulation of secretion of HCl into the lumen of the gastric gland. Similar connections may be detectable in other secretory cells and tissues. 相似文献9.
《Journal of Physiology》1998,92(1):31-35
Perifused rat pancreatic islets, prelabelled with 45Ca, were exposed for 90 min to a medium containing 30 mM K+, 0.25 mM diazoxide and 0.5 mM EGTA, but deprived of CaCl2. Either verapamil (0.05 mM) or Cd2+ (0.05 mM) were also present in the perifusate. Under these conditions a rise in D-glucose concentrations from either 2.8 to 16.7 mM or zero to 8.3 mM increased both 45Ca outflow and insulin release, after an initial and transient decrease in effluent radioactivity. These findings suggest that, in islets depolarised by exposure to a high extracellular concentration of K+, D-glucose provokes an intracellular redistribution of Ca2+ ions and subsequent stimulation of insulin release. The functional response to D-glucose is apparently not attributable to either the closing of ATP-sensitive K+ channels, which were actually activated by diazoxide, or stimulation of Ca2+ influx, which was prevented by the absence of extracellular Ca2+. The present experimental design thus reveals a novel component of the glucose-induced remodelling of Ca2+ fluxes in islet cells. Such an effect might also be operative under physiological conditions, when the hexose leads to depolarisation of the islet B-cells. 相似文献
10.
The transport of Zn2+, Co2+ and Ni2+ into yeast cells 总被引:10,自引:0,他引:10
11.
A rise in intracellular Ca2+(Ca2+in) concentration from 1 to 100 microM is accompanied by a 100-fold increase of erythrocyte membrane permeability for k+ (opening of k+-channels) as well as by membrane hyperpolarization. Both effects are partly inhibited by trifluoroperazine and completely by calmidozolium (R24571). The Ca2+-dependencies of erythrocyte permeability for K+ and of Ca2+ binding to calmodulin are in good correlation. Within the same range of Ca2+in concentrations, i.e. 1-100 microM the activity of Na+-pump decreases by 90% despite the presence of trifluoroperazine and R24571. The permeability of erythrocytes for o-phosphate anions diminishes 15-fold after addition of the anionic exchanger SITS inhibitor. The SITS-inhibited component decreases 9-10 times with a rise in Ca2+in from 10 and 100 microM. In the presence of trifluoroperazine and R24571 the sensitivity of the anionic exchanger towards Ca2+ shows a 2-3 increase. The increase in Ca2+in up to 100 microM is concomitant with the activation of 32Pi incorporation into band 4.1 protein. The effect of Ca2+in on the phosphorylation of this protein is inhibited by calmodulin inhibitors. Addition of protein kinase C activator (4 beta-phorbol-12 beta-myristate-13-acetate) also leads to the increased incorporation of 32P into band 4.1 protein, whereas protein kinase A activator (dibutyryl-cAMP) causes 32P incorporation into bands 4.1 and 5 proteins. No effect of protein kinase activators on the activity of Na+-pump as well as on the permeability of erythrocyte membranes for K+ and anions was revealed. The data obtained point to the differences in the mechanisms of Ca2+in involvement in the regulation of the above ion transport systems. Presumably, none of the mechanisms is coupled with modification of the level of cytoskeleton protein phosphorylation. The effect of Ca2+ is mediated by the Ca2+ interaction with calmodulin only in the case of K+-channels. 相似文献
12.
Alp Özgün Bora Garipcan 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》2021,1868(9):119062
Chronic exposure to magnetic fields (MFs) has a diverse range of effects on biological systems but definitive molecular mechanisms of the interaction remain largely unknown. One of the most frequently reported effects of MF exposure is an elevated concentration of intracellular Ca2+ through disputed pathways. Other prominent effects include increased oxidative stress and upregulation of neural markers through EGFR activation in stem cells. Further characterization of cascades triggered by MF exposure is hindered by the phenotype diversity of biological models used in the literature. In an attempt to reveal more mechanistic data in this field, we combined the most commonly used biological model and MF parameters with the most commonly reported effects of MFs.Based on clues from the pathways previously defined as sensitive to MFs (EGFR and Zn2+-binding enzymes), the roles of different types of channels (voltage gated Ca2+ channels, NMDA receptors, TRP channels) were inquired in the effects of 50 Hz MFs on bone marrow-derived mesenchymal stem cells. We report that, an influx of Zn2+ accompanies MF-induced Ca2+ intake, which is only attenuated by the broad-range inhibitor of TRP channels and store-operated Ca2+ entry (SOCE), 2-Aminoethoxydiphenyl borate (2-APB) among other blockers (memantine, nifedipine, ethosuximide and gabapentin). Interestingly, cation influx completely disappears when intracellular Zn2+ is chelated. Our results rule out voltage gated Ca2+ channels as a gateway to MF-induced Ca2+ intake and suggest Zn2+-related channels as a new focus in the field. 相似文献
13.
Nicholas T. Ktistakis 《BioEssays : news and reviews in molecular, cellular and developmental biology》1998,20(6):495-504
A variety of signalling molecules has been implicated over the past 8 years in the regulation of intracellular transport pathways. Those molecules include heterotrimeric GTP binding proteins, members of the protein kinase C family, and members of the Rho subfamily of small GTPases. Until recently, no common theme among the three classes of regulators was apparent. The finding that all three can influence the activity of phospholipase D (PLD), and the fact that members of the Arf subfamily of GTPases (with established roles in intracellular transport) are potent activators of PLD suggests the hypothesis that PLD is a focal point for integration of cellular responses to hormone signalling and for membrane homeostasis. Work during the past 2 years is beginning to uncover some transport pathways where PLD involvement is inferred. It is proposed that, if signalling is required to monitor and adjust transport rates to and from the various membrane organelles, the most economical way to achieve this would be to regulate recycling and allow the concentration of cargo receptors to determine forward transport. BioEssays 20 :495–504, 1998. © 1998 John Wiley & Sons, Inc. 相似文献
14.
Zoghbi ME Copello JA Villalba-Galea CA Vélez P Diaz Sylvester PL Bolaños P Marcano A Fill M Escobar AL 《Cell calcium》2004,36(2):119-134
The regulation of the Ca2+ -induced Ca2+ release (CICR) from intracellular stores is a critical step in the cardiac cycle. The inherent positive feedback of CICR should make it a self-regenerating process. It is accepted that CICR must be governed by some negative control, but its nature is still debated. We explore here the importance of the Ca2+ released from sarcoplasmic reticulum (SR) on the mechanisms that may control CICR. Specifically, we compared the effect of replacing Ca2+ with Sr2+ on intracellular Ca2+ signaling in intact cardiac myocytes as well as on the function of single ryanodine receptor (RyR) Ca2+ release channels in panar bilayers. In cells, both CICR and Sr2+ -induced Sr2+ release (SISR) were observed. Action potential induced Ca2+ -transients and spontaneous Ca2+ waves were considerably faster than their Sr2+ -mediated counterparts. However, the kinetics of Ca2+ and Sr2+ sparks was similar. At the single RyR channel level, the affinities of Ca2+ and Sr2+ activation were different but the affinities of Ca2+ and Sr2+ inactivation were similar. Fast Ca2+ and Sr2+ stimuli activated RyR channels equally fast but adaptation (a spontaneous slow transition back to steady-state activity levels) was not observed in the Sr2+ case. Together, these results suggest that regulation of the RyR channel by cytosolic Ca2+ is not involved in turning off the Ca2+ spark. In contrast, cytosolic Ca2+ is important in the propagation global Ca2+ release events and in this regard single RyR channel sensitivity to cytosolic Ca2+ activation, not low-affinity cytosolic Ca2+ inactivation, is a key factor. This suggests that the kinetics of local and global RyR-mediated Ca2+ release signals are affected in a distinct way by different divalent cations in cardiac muscle cells. 相似文献
15.
De novo biosynthesis of sphingolipids begins in the endoplasmic reticulum (ER) and continues in the Golgi apparatus and plasma membrane. A crucial step in sphingolipid biosynthesis is the transport of ceramide by vesicular and non-vesicular mechanisms from its site of synthesis in the ER to the Golgi apparatus. The recent discovery of the ceramide transport protein CERT has revealed a novel pathway for the delivery of ceramide to the Golgi apparatus for sphingomyelin (SM) synthesis. In addition to a ceramide-binding START domain, CERT has FFAT (referring to two phenylalanines [FF] in an acidic tract) and pleckstrin homology (PH) domains that recognize the ER integral membrane protein VAMP-associated protein (VAP) and Golgi-associated PtdIns 4-phosphate, respectively. Mechanisms for vectorial transport involving dual-organellar targeting and sites of deposition of ceramide in the Golgi apparatus are proposed. Similar Golgi-ER targeting motifs are also present in the oxysterol-binding protein (OSBP), which regulates ceramide transport and SM synthesis in an oxysterol-dependent manner. Consequently, this emerges as a potential mechanism for integration of sphingolipid and cholesterol metabolism. The identification of organellar targeting motifs in other related lipid-binding/transport proteins indicate that concepts learned from the study of ceramide transport can be applied to other lipid transport processes. 相似文献
16.
17.
Anion dependence of Ca2+ transport and (Ca2+ + K+)-stimulated Mg2+-dependent transport ATPase in rat pancreatic endoplasmic reticulum 总被引:2,自引:0,他引:2
T P Kemmer E Bayerd?rffer H Will I Schulz 《The Journal of biological chemistry》1987,262(28):13758-13764
Anion dependence of (Ca2+ + K+)-stimulated Mg2+-dependent transport ATPase and its phosphorylated intermediate have been characterized in both "intact" and "broken" vesicles from endoplasmic reticulum of rat pancreatic acinar cells using adenosine 5'-[gamma-32P] triphosphate ([gamma-32P]ATP). In intact vesicles (Ca2+ + K+)-Mg2+-ATPase activity was higher in the presence of Cl- or Br- as compared to NO3-, SCN-, cyclamate-, SO4(2-) or SO3(2-). Incorporation of 32P from [gamma-32P]ATP into the 100-kDa intermediate of this Ca2+ATPase was also higher in the presence of Cl-, Br-, NO3- or SCN- as compared to cyclamate-, SO4(2-) or SO3(2-). When the membrane permeability barrier to anions was abolished by breaking vesicle membrane with the detergent Triton X-100 (0.015%) (Ca2+ + K+)-Mg2+ATPase activity in the presence of weakly permeant anions, such as SO4(2-) and cyclamate-, increased to the level obtained with Cl-. However, 32P incorporation into 100-kDa protein was still higher in the presence of Cl- as compared to cyclamate-, indicating a direct effect of Cl- on the Ca2+ATPase molecule. The anion transport blocker 4,4-diisothiocyanostilbene-2,2-disulfonate (DIDS) inhibited (Ca2+ + K+)-Mg2+ATPase activity to about 10% of the Cl- stimulation level, irrespective of the sort of anions present in both intact and broken vesicles. This indicates a direct effect of DIDS on (Ca2+ + K+)-Mg2+ATPase. K+ ionophore valinomycin influenced (Ca2+ + K+)-Mg2+ATPase activity according to the actual K+ gradient: Ko+ greater than Ki+ caused inhibition, Ko+ less than Ki+ caused stimulation. From these results we conclude that Ca2+ transport into endoplasmic reticulum is coupled to ion movements which must occur to maintain electroneutrality. 相似文献
18.
In mammalian cells, phosphatidylserine (PtdSer) is synthesized through the action of the endoplasmic reticulum enzymes, PtdSer synthase 1 and 2, and the decarboxylation of PtdSer accounts for the majority of phosphatidylethanolamine (PtdEtn) synthesis. PtdSer decarboxylation for PtdEtn formation occurs in the mitochondria. In addition, the transport of PtdSer from the endoplasmic reticulum to the mitochondria is probably a rate limiting step for PtdEtn synthesis through the decarboxylation pathway. Therefore, the regulation of PtdSer synthesis and its intracellular transport appear to be essential events for the maintenance of normal cellular PtdSer and PtdEtn levels. Here we describe the current understanding of the regulation of PtdSer biosynthesis and the transport of PtdSer from the ER to the mitochondria in mammalian cells. 相似文献
19.
M Hilge 《The Journal of biological chemistry》2012,287(38):31641-31649
The binding of Ca(2+) to two adjacent Ca(2+)-binding domains, CBD1 and CBD2, regulates ion transport in the Na(+)/Ca(2+) exchanger. As sensors for intracellular Ca(2+), the CBDs form electrostatic switches that induce the conformational changes required to initiate and sustain Na(+)/Ca(2+) exchange. Depending on the presence of a few key residues in the Ca(2+)-binding sites, zero to four Ca(2+) ions can bind with affinities between 0.1 to 20 μm. Importantly, variability in CBD2 as a consequence of alternative splicing modulates not only the number and affinities of the Ca(2+)-binding sites in CBD2 but also the Ca(2+) affinities in CBD1. 相似文献
20.
D Kleiner 《Archives of biochemistry and biophysics》1974,165(1):121-125
Zn2+ ions linearly inhibit the electron transport in uncoupled mitochondria, Mg2+/ATP submitochondrial particles, and electron transport complex III between ubiquinone and the b cytochromes. A second effect is observed in coupled mitochondria only, where less than 4 μm Zn2+ causes a respiratory stimulation and a reduction of the b cytochromes; higher concentrations reverse these effects. The inhibition is completely reversed by chelating agents. The binding site has a unique affinity for Zn2+ with a dissociation constant of 1·10?6. 相似文献