共查询到20条相似文献,搜索用时 31 毫秒
1.
Göran Wingstrand 《Physiologia plantarum》1985,64(2):223-229
Membrane-bound MgATPase activity from roots of young sugar beet ( Beta vulgaris L. cv. Monohill) was investigated in a membrane fraction purified by partition in an aqueous polymer two-phase system. After two steps of "washing" with fresh bottom phase (rich in dextran), the polyethylene glycol rich top phase (U3 ) was practically free of mitochondrial membranes (cytochrome oxidase), and the remaining MgATPase activity showed high substrate specificity for ATP. An optimum for the MgATPase activity was found at pH 7. The activation by Na+ or K+ was strongest on the acid side without any observable shift in pH optimum. Oligomycin had no effect, but vanadate strongly inhibited the U3 MgATPase and the K+ activation was lost. The complex activation pattern achieved by varying the Na+ /K+ ratio at constant total concentration was interpreted as a synergistic (Na+ + K+ )-activation. The U3 fraction MgATP-ase activity showed a 4-fold increase in the presence of 0.01% Triton X-100 implying that the MgATPase activity is located in vesicles of which 75% or more are sealed with the ATP binding site on the inside. Comparison with the properties of plasma membrane. ATPases from other plants indicated that the U3 fraction MgATPase was mainly of plasma membrane origin. 相似文献
2.
Zinc-dependent changes in ESR signals, NADPH oxidase and plasma membrane permeability in cotton roots 总被引:9,自引:0,他引:9
The effect of Zn2+ on the plasma membrane permeability and superoxide radical (O2 - ) formation in roots was studied with cotton ( Gossypium hirsutum L. cv. Delta-pine 15/21) plants grown in nutrient solution with different Zn2+ supply. Compared to Zn-sufficient plants, the plasma membrane permeability of Zn-deficient plants was increased as indicated by a 3-, 5- and 2.5-fold increase in root cell leakage of K+ , NO3 - and organic carbon compounds, respectively. Resupply of Zn2+ to Zn-deficient plants for 12 h substantially decreased this leakage. The effects of Zn2+ on membrane permeability were closely correlated with the levels of O2 - measured by electron spin resonance (ESR) spectroscopy in the microsomal membrane fraction and in the cytosol fraction of root cells. The amplitudes of the O2 - -derived Tiron ESR signal also coincided with a O2 - -generating oxidase activity which was strongly dependent on the presence of NADPH and FAD. The results suggest that Zn2+ directly affects the integrity of the plasma membrane, at least in part, by interfering with O2 - generation by a membrane-bound NADPH oxidase. 相似文献
3.
Anna-Maria Hartmann Peter Blaesse† Thorsten Kranz‡ Meike Wenz‡ Jens Schindler Kai Kaila† Eckhard Friauf‡ Hans Gerd Nothwang‡ 《Journal of neurochemistry》2009,111(2):321-331
In the majority of neurons, the intracellular Cl− concentration is set by the activity of the Na+ -K+ -2Cl− cotransporter (NKCC1) and the K+ -Cl− cotransporter (KCC2). Here, we investigated the cotransporters' functional dependence on membrane rafts. In the mature rat brain, NKCC1 was mainly insoluble in Brij 58 and co-distributed with the membrane raft marker flotillin-1 in sucrose density flotation experiments. In contrast, KCC2 was found in the insoluble fraction as well as in the soluble fraction, where it co-distributed with the non-raft marker transferrin receptor. Both KCC2 populations displayed a mature glycosylation pattern. Disrupting membrane rafts with methyl-β-cyclodextrin (MβCD) increased the solubility of KCC2, yet had no effect on NKCC1. In human embryonic kidney-293 cells, KCC2 was strongly activated by a combined treatment with MβCD and sphingomyelinase, while NKCC1 was inhibited. These data indicate that membrane rafts render KCC2 inactive and NKCC1 active. In agreement with this, inactive KCC2 of the perinatal rat brainstem largely partitioned into membrane rafts. In addition, the exposure of the transporters to MβCD and sphingomyelinase showed that the two transporters differentially interact with the membrane rafts. Taken together, membrane raft association appears to represent a mechanism for co-ordinated regulation of chloride transporter function. 相似文献
4.
Carlos B. Duarte Luis M. Rosario Cristina M. Sena Arsélio P. Carvalho 《Journal of neurochemistry》1993,60(3):908-913
Abstract: In adrenal chromaffin cells, depolarization-evoked Ca2+ influx and catecholamine release are partially blocked by blockers of L-type voltage-sensitive Ca2+ channels. We have now evaluated the sensitivity of the dihydropyridine-resistant components of Ca2+ influx and catecholamine release to a toxin fraction (FTX) from the funnel-web spider poison, which is known to block P-type channels in mammalian neurons. FTX (1:4,000 dilution, with respect to the original fraction) inhibited K+ -depolarization-induced Ca2+ influx by 50%, as monitored with fura-2, whereas nitrendipine (0.1–1 μ M ) and FTX (3:3), a synthetic FTX analogue (1 m M ), blocked the [Ca2+ ]i transients by 35 and 30%, respectively. When tested together, FTX and nitrendipine reduced the [Ca2+ ]i transients by 70%. FTX or nitrendipine reduced adrenaline and noradrenaline release by ∼80 and 70%, respectively, but both substances together abolished the K+ -evoked catecholamine release, as measured by HPLC. The ω-conotoxin GVIA (0.5 μ M ) was without effect on K+ -stimulated 45 Ca2+ uptake. Our results indicate that FTX blocks dihydropyridine- and ω-conotoxin-insensitive Ca2+ channels that, together with L-type voltage-sensitive Ca2+ channels, are coupled to catecholamine release. 相似文献
5.
Plasmalemma was isolated from the roots of 2-week-old cucumber plants ( Cucumis sativus L. cv. Rhensk druv) by utilizing an aqueous polymer two-phase system with 6.5%:6.5% (w/w) Dextran T500 and polyethylene glycol (PEG) 3350 at pH 7.8. The plasmalemma fraction comprised ca 6% of the membrane proteins contained in the microsomal fraction. The specific activity of the plasma membrane marker enzyme (K+ , Mg2+ -ATPase) was 14- to 17-times higher in the upper (PEG-rich) than in the lower (Dextran-rich) phase, and the reverse was true for marker enzymes (cytochrome c oxidase, EC 1.9.3.1, and antimycin A-resistant NADPH cytochrome c reductase) of intracellular membranes. The ATPase was highly stimulated by the addition of detergent (Triton X-100), so that the isolated plasmalemma vesicles appear tightly sealed and in a right-side-out orientation. Further characterization of the ATPase activities showed a pH optimum at 6.0 in the presence of Mg2+ . This optimum was shifted to pH 5.8 after addition of K+ . K+ stimulated the ATPase activity below pH 6 and inhibited above pH 6. The ATPase activity was specific for ATP and sensitive to N,N-dicyclohexylcarbodiimide and sodium vanadate, with K+ enhancing the vanadate inhibition. The enzyme was insensitive to sodium molybdate, NO− 3 , azide and oligomycin. No Ca2+ -ATPase was detected, and even as little as 0.05 m M Ca2+ inhibited the Mg2+ -ATPase activity. 相似文献
6.
The inhibitory action of divalent cations on the Ca2+ -ATPase activity of a plasma membrane-rich microsome fraction isolated from the roots of barley ( Hordeum vulgare L. cv. Conquest) was investigated. Using electron paramagnetic resonance spectroscopy to measure cation-induced changes in membrane lipid properties, it was demonstrated that certain divalent cations (Ca2+ , Cd2+ , UO2+ 2 ) inhibit the Ca2+ ATP-ase by restriction of lipid polar head group mobility and not by alteration of membrane surface potential. Monovalent cations which stimulate the Ca2+ -ATPase of barley roots (Na+ , K+ , ethanolamine HCl) can also reverse the Ca2+ -ATPase inhibition by Cd2+ . The degree of Na+ reversal of Cd2+ -induced Ca2+ -ATPase inhibition was influenced by the nature of the anion. 相似文献
7.
Ozone tolerance in snap bean is associated with elevated ascorbic acid in the leaf apoplast 总被引:6,自引:0,他引:6
Ascorbic acid (AA) in the leaf apoplast has the potential to limit ozone injury by participating in reactions that detoxify ozone and reactive oxygen intermediates and thus prevent plasma membrane damage. Genotypes of snap bean ( Phaseolus vulgaris L) were compared in controlled environments and in open-top field chambers to assess the relationship between extracellular AA content and ozone tolerance. Vacuum infiltration methods were employed to separate leaf AA into extracellular and intracellular fractions. For plants grown in controlled environments at low ozone concentration (4 nmol mol−1 ozone), leaf apoplast AA was significantly higher in tolerant genotypes (300–400 nmol g−1 FW) compared with sensitive genotypes (approximately 50 nmol g−1 FW), evidence that ozone tolerance is associated with elevated extracellular AA. For the open top chamber study, plants were grown in pots under charcoal-filtered air (CF) conditions and then either maintained under CF conditions (29 nmol mol−1 ozone) or exposed to elevated ozone (67 nmol mol−1 ozone). Following an 8-day treatment period, leaf apoplast AA was in the range of 100–190 nmol g−1 FW for all genotypes, but no relationship was observed between apoplast AA content and ozone tolerance. The contrasting results in the two studies demonstrated a potential limitation in the interpretation of extracellular AA data. Apoplast AA levels presumably reflect the steady-state condition between supply from the cytoplasm and utilization within the cell wall. The capacity to detoxify ozone in the extracellular space may be underestimated under elevated ozone conditions where the dynamics of AA supply and utilization are not adequately represented by a steady-state measurement. 相似文献
8.
Protein kinases in plants have not been examined in detail, but protein phosphorylation has been shown to be essential for regulating plant growth via the signal transduction system. A Ca2+ - and phospholipid-dependent protein kinase, possibly involved in the intracellular signal transduction system from rice leaves, was partially purified by sequential chromatography on DE52, Phenyl Superose and Superose 12. This protein kinase phosphorylated the substrate, histone III-S, in the presence of Ca2+ and phosphatidylserine. The apparent molecular mass of the Ca2+ - and phosphatidylserine-dependent protein kinase (Ca2+ /PS PK), determined by phosphorylation in SDS-polyacrylamide gel containing histone III-S, was 50 kDa. The protein kinase differed from Ca2+ -dependent protein kinase (CDPK) in rice leaves in that Ca2+ /PS PK showed phospholipid dependency and the molecular mass of Ca2+ /PS PK exceeded that of CDPK. Investigations were carried out on changes in Ca2+ /PS PK and CDPK activity in the cytosolic and membrane fractions during germination. The maximum activity of Ca2+ /PS PK in the cytosolic fraction was observed before imbibition and that of CDPK in the membrane fraction was noted at 6 days following imbibition. Protein kinases are likely to regulate plant growth through protein phosphorylation. 相似文献
9.
Root ammonium transport efficiency as a determinant in forest colonization patterns: an hypothesis 总被引:3,自引:0,他引:3
H. J. Kronzucker M. Y. Siddiqi A. D. M. Glass D. T. Britto 《Physiologia plantarum》2003,117(2):164-170
Ratios of ammonium (NH4 + ) to nitrate (NO3 – ) in soils are known to increase during forest succession. Using evidence from several previous studies, we hypothesize that a malfunction in NH4 + transport at the membrane level might limit the persistence of early successional tree species in later seral stages. In those studies, 13 N radiotracing was used to determine unidirectional fluxes and pool sizes of NH4 + and NO3 – in seedlings of the late-successional species white spruce ( Picea glauca ) and in the early successional species Douglas-fir ( Pseudotsuga menziesii var. glauca ) and trembling aspen ( Populus tremuloides ). At high external NH4 + , the two early successional species accumulated excessive NH4 + in the root cytosol, and exhibited high-velocity, low-efficiency (15% to 22%), membrane fluxes of NH4 + . In sharp contrast, white spruce had low cytosolic NH4 + accumulation, and lower-velocity but much higher-efficiency (65%), NH4 + fluxes. Because these divergent responses parallel known differences in tolerance and toxicity to NH4 + amongst these species, we propose that they constitute a significant driving force in forest succession, complementing the discrimination against NO3 – documented in white spruce (Kronzucker et al. 1997). 相似文献
10.
Physiological and biochemical modifications induced by Fe-deficiency have been studied in cucumber ( Cucumis sativus L. cv. Marketer) roots, a Strategy I plant that initiates a rapid acidification of the medium and an increase in the electric potential difference when grown under Fe-deficiency. Using the aqueous two-phase partitioning method, a membrane fraction which has the plasmalemma characteristics was purified from roots of plants grown in the absence and in the presence of iron. The plasma membrane vesicles prepared from Fe-deficient plants showed an H+ -ATPase activity (EC 3.6.1.35) that is twice that of the non-deficient control. Furthermore, membranes from Fe-deficient plants showed a higher capacity to reduce Fe3+ -chelates. The difference observed in the reductase activity was small with ferricyanide (only 30%) but was much greater with Fe3 -EDTA and Fe3 -citrate (210 and 250%, respectively). NADH was the preferred electron donor for the reduction of Fe3+ compounds. Fe3+ reduction in plasma membrane from cucumber roots seems to occur with utilisation of superoxide anion, since addition of superoxide dismutase (SOD; EC 1.15.1.1) "in vitro" decreased Fe3+ reduction by 60%.
The response and the difference induced by iron starvation on these two plasma membrane activities together with a possible involvement of O2 in controlling the Fe3+ /Fe2+ ratio in the rhizosphere are discussed. 相似文献
The response and the difference induced by iron starvation on these two plasma membrane activities together with a possible involvement of O
11.
Claude Penel Thomas Gaspar Michèle Crèvecoeur Claire Kevers Hubert Greppin 《Physiologia plantarum》1990,79(2):250-254
Ca2+ and Mn2+ activate the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) by root microsomes of Vicia lens as they do in other similar systems. The preparation of microsomes in the presence of Mn2+ greatly increases their ability to convert ACC into ethylene, without addition of Mn2+ in the reaction mixture. Ca2+ does not have this property. The effect could not be attributed to Mn2+ entrapping into membrane vesicles (sonication followed by repelleting had no effect) but, possibly, in part to Mn2+ -mediated binding to microsomes of a soluble factor favouring the conversion of ACC to C2 H4 . Although no direct correlation could be established in vitro between ethylene-forming-enzyme (EFE) and peroxidase activities, some soluble peroxidases might be this soluble factor. Mn2+ favoured attachment to membranes of some peroxidase activity from the soluble fraction and from commercial HRP and lipoxygenase. This binding effect of Mn2+ cannot be readily distinguished from its role in the generation of a chain of free radicals and in redox mechanisms. 相似文献
12.
Possible Mechanism of Dantrolene Stabilization of Cultured Neuroblastoma Cell Plasma Membranes 总被引:2,自引:0,他引:2
Teruo Hayashi Ariyuki Kagaya Nobutaka Motohashi Shigeto Yamawaki 《Journal of neurochemistry》1994,63(5):1849-1854
Abstract: Some reports have suggested that dantrolene interacts directly with the membrane bilayer. We investigated effects of dantrolene on changes in membrane properties induced by compound 48/80 (C48/80), a membrane stimulator. The addition of C48/80 for 1 min elicited a rapid, dose-dependent Ca2+ influx, which was reduced to 14% by the absence of external Ca2+ . Dantrolene inhibited the C48/80-induced increase in Ca2+ permeability of plasma membranes in a concentration-dependent manner (0.33–10 µ M , IC50 value was 5 µ M ). We next examined C48/80-induced changes in structural and dynamic membrane properties by electron spin resonance (ESR). The ratio h 0 / h −1 was determined to evaluate membrane fluidity. C48/80 increased the membrane fluidity in a concentration-dependent manner (0.1–0.56 mg/ml). Dantrolene (10 µ M ) itself did not change the membrane fluidity, but it significantly reduced the C48/80-induced increase in membrane fluidity (0.56 mg/ml). Moreover, the C48/80-induced increase in fluidity was dependent on extracellular Ca2+ . We conclude that dantrolene protects neuroblastoma cell plasma membrane from C48/80-induced membrane perturbation, which causes Ca2+ influx and an increase in membrane fluidity. These findings strongly suggest that dantrolene directly stabilizes the neuronal plasma membrane. 相似文献
13.
ROBERTO DOCAMPOA FERNANDA R. GADELHA SILVIA N. J. MORENO GUSTAVO BENAIM MARIA E. HOFFMANN ANIBAL E. VERCESI 《The Journal of eukaryotic microbiology》1993,40(3):311-316
ABSTRACT. We have demonstrated previously that crystal violet induces a rapid, dose-related collapse of the inner mitochondrial membrane potential of Trypanosoma cruzi epimastigotes. In this work, we show that crystal violet-induced dissipation of the membrane potential was accompanied by an efflux of Ca2+ from the mitochondria. In addition, crystal violet inhibited the ATP-dependent, oligomycin-, and antimycin A-insensitive Ca2+ uptake by digitonin-permeabilired epimastigotes. Crystal violet also induced Ca2+ release from the mitochondria and endoplasmic reticulum of digitonin-permeabilized trypomastigotes. Furthermore, crystal violet inhibited Ca2+ uptake and the (Ca2+ -Mg2+ )ATPase of a highly enriched plasma membrane fraction of epimastigotes, thus indicating an inhibition of other calcium transport mechanisms of the cells. Disruption of Ca2+ homeostasis by crystal violet may be a key process leading to trypanosome cell injury by this drug. 相似文献
14.
Abstract— Three different types of p -nitrophenyl phosphatases (NPPases) were solubilized by deoxycholate treatment from a membrane fraction of bovine cerebral cortex, and their characteristics were determined. Of these three NPPases (acid, Mg2+ -activated, and K+ , Mg2+ -activated), only K-Mg NPPase was stimulated about two-fold by phospholipid and was inhibited by unsaturated neutral lipids and fatty acids. Unlike Na+ -K+ -Mga+ -activated ATPase, the enzyme did not absolutely require phospholipid for its activity, but was similarly thermolabile and was protected by phospholipid from thermal inactivation. Acid NPPase was separable from the other two NPPases by ammonium sulphate fractionation, and partly solubilized by dialysis against ATP-mercaptoethanol solution. Hg2+ inhibited equally all three NPPases, but Ca2+ inhibited only Mg and K-Mg NPPases. Ouabain was effective on K-Mg NPPase alone. 相似文献
15.
Abstract: A novel fluorescent Na+ indicator, Na+ -binding benzofuran isophthalate (SBFI), was used to follow changes in the intracellular free Na+ concentration ([Na+ ]1 ) of synaptosomes. The dye, when loaded into synapto- somes in the form of its acetoxymethyl ester, was responsive to changes of [Na+ ]1 . Calibration was made using the 340/380 nm excitation ratio when the cytoplasmic Na+ concentration was equilibrated with different concentrations of extracellular Na+ in the presence of 2 μ M gramicidin D. The basal value of [Na+ ]1 in synaptosomes in the presence of 140 m M extracellular Na+ was found to be 10.9 ± 1.8 m M. Veratridine, which opens potential-dependent Na+ channels, caused a sudden increase in [Na+ ]1 in a concentration-dependent manner (1 -20 μ M ), whereas the effect of ouabain (20 and 50 μ M ), the inhibitor of the plasma membrane Na+ ,K+ -ATPase, was more gradual. The rise in the fluorescence intensity upon addition of veratridine was prevented completely by 2 μ M tetrodotoxin. α-Latrotoxin, the black widow spider toxin, caused an increase in the fluorescence intensity, which became evident 1 min after the addition of the toxin. The rate of increase was proportional to the concentration of the toxin (0.19–1.5 n M ). This report confirms our earlier finding demonstrating a Na+ -dependent component in the action of α-Iatrotoxin, and shows that changes in [Na+ ]1 in synaptosomes can be followed by SBFI. 相似文献
16.
F. B. Jensen† J. Brahm‡ P. Koldkjær§ T. Wang¶ D. J. McKenzie E. W. Taylor 《Journal of fish biology》2003,62(5):1044-1052
Carbon dioxide transport in African lungfish Protopterus aethiopicus blood conformed to the typical vertebrate scheme, implying a crucial and rate-limiting role of erythrocyte Cl– /HCO3 – exchange. The rate coefficient for unidirectional Cl– efflux via the anion exchanger ( k , s−1 ) increased with temperature in African lungfish, but values were well below those reported in other species. The erythrocytes of African lungfish were, however, very large (mean cellular volume = 6940 µm3 ), and the ratio of cell water volume to membrane surface area was high ( V w A m −1 = 1·89). Hence, the apparent Cl– permeability ( P Cl = kV w A m −1 , µm s−1 ) was close to that in other vertebrates. The plot of ln P Cl against the inverse absolute temperature was left-shifted in the tropical African lungfish compared to the temperate rainbow trout Oncorhynchus mykiss , which supports the idea that P Cl is similar among animals when compared at their preferred temperatures. Also, Q 10 for anion exchange calculated from P Cl values in African lungfish was 2·0, supporting the idea that the temperature sensitivity of erythrocyte anion exchange matches the temperature sensitivity of CO2 production and transport in ectothermic vertebrates. 相似文献
17.
Intracellular concentrations of Na+ and K+ were similar (∼75 mmol l−1 ) in rainbow trout Oncorhynchus mykiss hepatocytes directly following isolation by collagenase digestion, but partial recovery occurred over 6 h with K+ levels increasing to 110 mmol l−1 and Na+ levels decreasing to 42 mmol l−1 . Black bullhead Ameiurus melas hepatocytes exhibited higher intracellular concentrations of K+ (90 mmol l−1 ) than Na+ (55 mmol l−1 ) with no recovery occurring over 6 h following cell isolation. Concentrations of Na+ , K+ and Cl− in eel Anguilla rostrata hepatocytes were similar (∼ 55 mmol l−1 ) following isolation, with no recovery occurring over time. Erythrocytes from all species apparently did not experience an intracellular ion imbalance following isolation as indicated by high K+ levels (<140 mmol l−1 ) and low Na+ levels (<40 mmol l−1 ) during the entire 24-h monitoring period. Although hepatocytes from all species exhibited an ion imbalance post-isolation, comparison of their in vitro intracellular Na+ and K+ concentrations with those in plasma demonstrated that directionally correct ion gradients still exist across the cell membrane, albeit differing from those that would be found in the tissue in vivo . 相似文献
18.
A microsomal fraction was prepared by differential centrifugation from the homogenate of dark grown shoots of oats ( Avena sativa L. cv. Sol II). Plasma membranes were prepared from the microsomal fraction by means of an aqueous polymer two phase partition method. The content of phytochrome in the microsomal fraction and the plasma membrane fraction, respectively, were studied after different irradiation treatments of the intact shoots. Red irradiation increased the content of phytochrome in both the microsomal and plasma membrane fraction, especially in the presence of Mg2+ . The increase induced by red light was fully reversible by far-red light for the plasma membrane fraction both in the presence and absence of Mg2+ , in contrast to the microsomal fraction where Mg2+ had to be omitted. KI treatment of the membranes destroyed the binding of phytochrome whereas agents such as KCI, EDTA, CaCl2 and Triton X-100, did not have this effect, indicating that the phytochrome attachment to the membrane is hydrophobic. This in vivo binding resembles to a large extent the one obtained in vitro by Sundqvist and Widell (Physiol. Plant. 59: 35–41, 1983) even though some differences between the phytochrome species and the membrane side exposed probably occur; so that the present interaction between phytochrome and the plasma membrane does not necessarily reflect the interaction that leads to physiological responses, and there could be more than one type of interaction. 相似文献
19.
Short-term thermal acclimation induces adaptive changes in the inner mitochondrial membranes of fish skeletal muscle 总被引:1,自引:0,他引:1
In the oxidative muscles (musculi laterales superficiales) of crucian carp Carassius carassius acclimated for 6 weeks to either 5 or 25° C, the volume density and the surface density of fibres per tissue did not differ significantly between the control and experimental groups. The correlation ratio (μ2 ) for these values was below 50, 39·3 and 43·9 respectively. After acclimation to 5° C, the surface density of outer mitochondrial membrane per fibre increased significantly from 0·93 to 1·23m2 cm−3 in the summer population but dropped from 0·94 to 0·67 m2 cm−3 in the winter population. The surface density of outer mitochondrial membrane per mitochondrion increased from 3·24 to 4·52 m2 cm−3 in summer fish. After acclimation to 25° C, the surface density of inner mitochondrial membranes per muscle fibre decreased from 4·04 to 1·79 m2 cm−3 in summer fish and from 3·86 to 1·07 m2 cm−3 in winter fish. The surface density of inner mitochondrial membranes per mitochondrion increased from 14·17 to 15·60 m2 cm−3 in summer fish but dropped from 13·91 to 10·67 m2 cm−3 in winter fish. Correlation matrices demonstrate a negative correlation of the surface density of outer mitochondrial membrane per mitochondrion with the volume density of mitochondria per fibre and temperature, suggesting cold-induced proliferation of small mitochondria. It was concluded that short-term cold acclimation increased surface area of the inner mitochondrial membranes in summer fish. 相似文献
20.
Abstract: The Na+ /Ca2+ exchanger is an important element in the maintenance of calcium homeostasis in bovine chromaffin cells. The Na+ /Ca2+ exchanger from other cell types has been extensively studied, but little is known about its regulation in the cell. We have investigated the role of reversible protein phosphorylation in the activity of the Na+ /Ca2+ exchanger of these cells. Cells treated with 1 m M dibutyryl cyclic AMP (dbcAMP), 1 µ M phorbol 12,13-dibutyrate, 1 µ M okadaic acid, or 100 n M calyculin A showed lowered Na+ /Ca2+ exchange activity and prolonged cytosolic Ca2+ transients caused by depolarization. A combination of 10 n M okadaic acid and 1 µ M dbcAMP synergistically inhibited Na+ /Ca2+ exchange activity. Conversely, 50 µ M 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, a protein kinase inhibitor, enhanced Na+ /Ca2+ exchange activity. Moreover, we used cyclic AMP-dependent protein kinase and calcium phospholipid-dependent protein kinase catalytic subunits to phosphorylate isolated membrane vesicles and found that the Na+ /Ca2+ exchange activity was inhibited by this treatment. These results indicate that reversible protein phosphorylation modulates the activity of the Na+ /Ca2+ exchanger and suggest that modulation of the exchanger may play a role in the regulation of secretion. 相似文献