共查询到20条相似文献,搜索用时 15 毫秒
1.
Gabriella Sandri Gianluigi Sottocasa Enrico Panfili Gianfranco Liut 《生物化学与生物物理学报:生物膜》1979,558(2):214-220
Rat liver mitochondria may be subfractionated in sediment and supernatant fractions by swelling in the presence of EDTA and oxaloacetate. The sediment is largely depleted of the Ca2+-binding glycoprotein and its Ca2+-transporting activity may be as low as 10–20% of the starting value. Both the rate of Ca2+ uptake and the capacity to maintain a high Ca2+ concentration gradient across the membrane are depressed. Addition of an osmotic supernatant to the assay mixture may partially restore the original Ca2+-transporting ability. The active component in the supernatant is the Ca2+-binding glycoprotein. This is shown by the following facts: (a) the effect is enhanced by the addition of the purified glycoprotein to the supernatant; (b) precipitation of the glycoprotein from the supernatant by affinity chromatography-purified antibodies abolishes the stimulatory effect, and (c) in the presence of 130 μM Mg2+, the glycoprotein alone may restore fully the Ca2+-transporting ability of the particles. The maximal velocity is already reached at 0.1 μg glycoprotein/mg mitochondrial protein. 相似文献
2.
Calmodulin-depleted isotonic erythrocyte ghosts contain 200 ng residual calmodulin/mg protein which is not removed by extensive washings at pCa2+ > 7. Specific activity and Ca2+-affinity of the (Ca2+ + Mg2+)ATPase increase at increasing calmodulin, with K0.5 Ca of 0.38 μM at calmodulin concentrations corresponding to that in erythrocytes. High Ca2+ concentrations inhibit the enzyme. Specific activity and Ca2+-affinity of the enzyme decrease at increasing Mg2+ concentrations. The Ca2+ ? Mg2+ antagonism is likewise observed at inhibitory Ca2+ concentrations. 相似文献
3.
A method for the isolation of coupled mitochondria from the acellular slime mould Physarum polycephalum is described. The mitochondria oxidize respiratory substrates at rates comparable to those of mitochondria from other micro-organisms and show similar responses to respiratory inhibitors. ADP/O values approach similar values to those obtained with mitochondria from higher organisms: 3 with NAD-linked substrates, 2 with succinate, and 1 with ascorbate-TMPD.Mitochondria actively take up low concentrations of Ca2+ with stimulation of their respiration. With succinate or pyruvate-malate as substrates respiratory responses are depressed by Ca2+ concentrations in excess of 200 μM in the presence or absence of phosphate.Exogenous NADH is unique in supporting the uptake of large amounts of Ca2+ in the presence of phosphate and in showing an unusual ‘uncoupled’ response in the absence of phosphate.A sigmoidal relationship occurs between initial velocity of Ca2+ uptake and Ca2+ concentration with a maximum velocity of approx. 15 nmol/s per mg protein and half maximum velocity occurring at approx. 50 μM Ca2+. 相似文献
4.
Gerhard Meissner 《生物化学与生物物理学报:生物膜》1973,298(4):906-926
The binding of ATP and Ca2+ by the Ca2+ pump protein of sarcoplasmic reticulum from rabbit skeletal muscle has been studied and correlated with the formation of a phoshorylated intermediate. The Ca2+ pump protein has been found to contain one specific ATP and two specific Ca2+ binding sites per phosphorylation site. ATP binding is dependent on Mg2+ and is severely decreased when a phosphorylated intermediate is formed by the addition of Ca2+. In the presence of Mg2+ and the absence of Ca2+, ATP and ADP bind completely to the membrane. Pre-incubation with N-ethylmaleimide results in inhibition of ATP binding and decrease of Ca2+ binding. In the absence of ATP, Ca2+ binding is noncooperative at pH 6–7 and negatively cooperative at pH 8. Mg2+, Sr2+ and La3+, in that order, decrease Ca2+ binding by the Ca2+ pump protein. The affinity of the Ca2+ pump protein for both ATP and Ca2+ increases when the pH is raised from 6 to 8. At the infection point (pH ≈ 7.3) the binding constants of the Ca2+ pump protein-MgATP2? and Ca2+ pump protein-calcium complexes are approx. 0.25 and 0.5 μM?1, respectively. The unphosphorylated Ca2+ pump protein does not contain a Mg2+ binding site with an affinity comparable to those of the ATP and Ca2+ binding sites.The affinity of the Ca2+ pump protein for Ca2+ is not appreciably changed by the addition of ATP. The ratio of phosphorylated intermediate formed to bound Ca2+ is close to 2 over a 5-fold range of phosphoenzyme concentration. The equilibrium constant for phosphoenzyme formation is less than one at saturating levels of Ca2+. The phosphoenzyme is thus a “high-energy” intermediate, whose energy may then be used for the translocation of the two Ca2+.A reaction scheme is discussed showing that phosphorylation of sarcoplasmic reticulum proceeds via an enzyme-Ca22+-MgATP2? complex. This complex is then converted to a phosphoenzyme intermediate which binds two Ca2+ and probably Mg2+. 相似文献
5.
Yat H. Lau 《生物化学与生物物理学报:生物膜》1983,730(2):276-284
Ca2+ transport by sarcoplasmic reticulum vesicles was examined by incubating sarcoplasmic reticulum vesicles (0.15 mg/ml) at 37°C in, either normal medium that contained 0.15 M sucrose, 0.1 M KCl, 60 μM CaCl2, 2.5 mM ATP and 30 mM Tes at pH 6.8, or a modified medium for elimination of ADP formed from ATP hydrolysis by including, in addition, 3.6 mM phosphocreatine and 33 U/ml of creatine phosphokinase. In normal medium, Ca2+ uptake of sarcoplasmic reticulum vesicles reached a plateau of about 100 nmol/mg. In modified medium, after this phase of Ca2+ uptake, a second phase of Ca2+ accumulation was initiated and reached a plateau of about 300 nmol/mg. The second phase of Ca2+ accumulation was accompanied by phosphate uptake and could be inhibited by ADP. Since, under these experimental conditions, there was no significant difference of the rates of ATP hydrolysis in normal medium and modified medium, extra Ca2+ uptake in modified medium but not in normal medium could not be explained by different phosphate accumulation in the two media. Unidirectional Ca2+ influx of sarcoplasmic reticulum near steady state of Ca2+ uptake was measured by pulse labeling with 45Ca2+. The Ca2+ efflux rate was then determined by subtracting the net uptake from the influx rate. At the first plateau of Ca2+ uptake in normal medium, Ca2+ influx was balanced by Ca2+ efflux with an exchange rate of 240 nmol/mg per min. This exchange rate was maintained relatively constant at the plateau phase. In modified medium, the Ca2+ exchange rate at the first plateau of Ca2+ uptake was about half of that in normal medium. When the second phase of Ca2+ uptake was initiated, both the influx and efflux rates started to increase and reached a similar exchange rate as observed in normal medium. Also, during the second phase of Ca2+ uptake, the difference between the influx and efflux rates continued to increase until the second plateau phase was approached. In conditions where the formation of ADP and inorganic phosphate was minimized by using a low concentration of sarcoplasmic (7.5 μg/ml) and/or using acetyl phosphate instead of ATP, the second phase of Ca2+ uptake was also observed. These data suggest that the Ca2+ load attained by sarcoplasmic reticulum vesicles during active transport is modulated by ADP accumulated from ATP hydrolysis. ADP probably exerts its effect by facilitating Ca2+ efflux, which subsequently stimulates Ca2+ exchange. 相似文献
6.
The ultrastructure and 90 ° light-scattering capacity of adrenal cortex mitochondria have been examined under conditions which lead to an activation of malic enzyme activity in these mitochondria. After isolation, the mitochondria display an aggregate ultrastructure which does not resemble the vesicular (orthodox) form normally seen in vivo. Under conditions of malic enzyme activation (presence of malate, NADP+, Mg2+ and 1 mm Ca2+), the ultrastructure reverts to a vesicular form as seen in vivo. Of these required components, only Ca2+ affects the ultrastructure. The ultrastructural transformation from the aggregate to the orthodox form is always accompanied by a decrease in the 90 ° light-scattering capacity. When produced by Ca2+, transformation requires energy-dependent Ca2+ uptake if an oxidizable substrate is present. In the absence of substrate, the transformation occurs as an apparent energy-independent effect. Mn2+ can substitute for Ca2+ only in the presence of substrate. In de-energized mitochondria, Mn2+ prevents the effects of Ca2+. The activation of malic enzyme is always preceded by a decrease in light scattering and transformation to the orthodox ultrastructure; however, the presence of the orthodox form is not a sufficient condition since subsequent chelation of free Ca2+ fails to reverse either the decrease in light scattering or ultrastructural transformation but does reverse the enzyme activation. In addition, levels of Mn2+ which effectively depress light-scattering capacity and produce the orthodox form, fail to activate malic enzyme significantly. The data are discussed as they relate to Ca2+-induced damage in mitochondria. 相似文献
7.
Mitochondria isolated from the late-exponential non-shaken culture of the ciliate protozoan Tetrahymena pyriformis GL was investigated. The presence of energy-dependent Ca2+ transport system was shown. In the main the properties of this system have been essentially the same as in mitochondria of vertebrate organisms. The isolated mitochondria contained 23±5 ng-ion Ca2+ per mg of protein. The intramitochondrial free concentration of Ca2+ was measured in the presence of uncoupler FCCP with the use of fluorescent Ca2+ chelator chlortetracycline and null point titration method. In the absence of phosphate, free [Ca2+] varied from 1 to 2.5 mM depending on the internal Ca2+ content. In the presence of 2 mM phosphate, free [Ca2+]in has not exceeded 0.1–0.3 mM. It was shown that ruthenium red and Mg2+ in different manner have an inhibitory effect on Ca2+ transport. Besides this, Mg2+ also has a stabilizing effect on mitochondria, possibly, by preventing passive ions leaks across the membrane. 相似文献
8.
The effect of Sr2+ on the set point for external Ca2+ was studied in rat heart and liver mitochondria with the aid of a Ca2+-sensitive electrode. In respiring mitochondria the set point is determined by the rates of Ca2+ influx on the Ca2+ uniporter and efflux by various mechanisms. We studied the Ca2+-Na+ exchange pathway in heart mitochondria and the Δψ-modulated efflux pathway in liver mitochondria. Prior accumulation of Sr2+ was found to shift the set points towards lower external Ca2+ both in heart mitochondria under conditions of Ca2+-Na+ exchange and in liver mitochondria under conditions that should promote opening of the Δψ-modulated pathway. The effect on the set point was found to be due to inhibition of Ca2+ efflux by Sr2+ taken up by the mitochondria, while Sr2+ efflux was too slow to be measurable. 相似文献
9.
Ernesto Carafoli Marina Gavilanes Hubert Affolter Marietta Tuena de Gómez-Puyou Armando Gómez-Puyou 《Cell calcium》1980,1(4):255-265
The ATP-supported Ca2+ uptake of heart and liver mitochondria preincubated in conditions in which electron transport had either been prevented by rotenone or antimycin, or induced by oxidizable substrates, has been studied. Mitochondria preincubated with respiratory inhibitors accumulate Ca2+ less efficiently than mitochondria preincubated with oxidizable substrates. The difference correlates with the degree of activation of the oligomycin-sensitive ATPase. The results indicate that the rate at which mitochondria take up Ca2+ in the ATP-supported system may be controlled by the reversible asociation of the inhibiting peptide (Pullman,. and Monroy, J. Biol. Chem., 238, 3762–3769) with the ATPase complex. Since this process appears to be modulated by the transmembrane electrochemical gradient, the latter may regulate the uptake of Ca2+ in a hitherto undescribed way. 相似文献
10.
E. Carafoli R. Dabrowska F. Crovetti R. Tiozzo W. Drabikowski 《Biochemical and biophysical research communications》1975,62(4):908-912
Rat heart mitochondria are able to extract a large fraction of the Ca2+ tightly bound to rabbit skeletal muscle troponin, or to the 18.300 daltons, Ca2+ receptor fragment of the troponin molecule (TN-C). The amount of Ca2+ removed may reach 100% in the case of TN-C- but substantially less with intact troponin. The reaction is fairly rapid, often reaching completion in seconds, and is inhibited by uncouplers and by the classical inhibitor of Ca2+ transport in mitochondria, ruthenium red. 相似文献
11.
Ca2+ stimulates the binding of a variety of prostaglandins (PG) to liver mitochondria. Optimal binding is observed at slightly acidic pH and at concentrations of Ca2+ between 200 and 500 μm. The stimulation of the binding requires the active transport of Ca2+ in mitochondria and is only observed in the absence of permeant anions. The maximal amount of PG bound is about 3 nmol/mg of mitochondrial protein. All PG tested induce efflux of the Ca2+ taken up by mitochondria without impairing the ability of mitochondria to actively accumulate it. Optimal stimulation of the efflux of Ca2+ requires concentrations of PG higher than those used in the PG-binding experiments and is associated with an evident uncoupling of the respiration that follows a Ca2+-induced O2 uptake jump. The “uncoupling” by PG is explained by postulating the entrance of protonated PG into mitochondria, followed by their exit from the organelle as 2:1 complexes with Ca2+. 相似文献
12.
Ca2+ efflux from sarcoplasmic reticulum vesicles was studied by measurements of net Ca2+ uptake, 45Ca2+ flux and hydrolysis of energy-rich phosphate. The maximal Ca2+ uptake capacity (150–200 nmol/mg protein at pH 6.7, 10 mM MgCl2 and μ=0.26) was independent of the nature and concentration of the energy-donating substrate (ATP or carbamyl phosphate) and of temperature (15–35°C), suggesting coupling between influx and efflux of Ca2+. In the presence of high concentrations of ATP, this efflux of Ca2+ was much higher than the passive Ca2+ permeation, measured after ATP or Ca2+ depletion of the reaction medium. Ca2+ efflux was imperceptible at vesicle filling levels below 35–40 nmol Ca2+/mg protein, and uncorrelated to the inhibition of the Ca2+-ATPase by high intravesicular Ca2+ concentrations. Analysis of the data indicated that Ca2+ efflux under our conditions probably is associated with one of the Ca2+-ATPase partial reactions occurring after dephosphorylation, rather than with a reversal of the Ca2+ translocation step in the phosphorylated state of the enzyme. Furthermore, passive Ca2+ permeation may be concurrently reduced during the enzymatically active state. It is proposed that both Ca2+ efflux and passive Ca2+ permeation (Ca2+ outflow) proceed via the same channels which are closed (occluded) during part of the Ca2+-ATPase reaction cycle. 相似文献
13.
Joseph D. Robinson 《Journal of neurochemistry》1981,37(1):140-146
Abstract: With a partially purified, membrane-bound (Ca + Mg)-activated ATPase preparation from rat brain, the K0.5 for activation by Ca2+ was 0.8 p μm in the presence of 3 mm -ATP, 6 mm -MgCl2, 100 mM-KCI, and a calcium EGTA buffer system. Optimal ATPase activity under these circumstances was with 6-100 μm -Ca2+, but marked inhibition occurred at higher concentrations. Free Mg2+ increased ATPase activity, with an estimated K0.5, in the presence of 100 μm -CaCl2, of 2.5 mm ; raising the MgCl2 concentration diminished the inhibition due to millimolar concentrations of CaCl2, but antagonized activation by submicromolar concentrations of Ca2+. Dimethylsulfoxide (10%, v/v) had no effect on the K0.5 for activation by Ca2+, but decreased activation by free Mg2+ and increased the inhibition by millimolar CaCl2. The monovalent cations K+, Na+, and TI+ stimulated ATPase activity; for K+ the K0.5 was 8 mm , which was increased to 15 mm in the presence of dimethylsulfoxide. KCI did not affect the apparent affinity for Ca2+ as either activator or inhibitor. The preparation can be phosphorylated at 0°C by [γ-32P]-ATP; on subsequent addition of a large excess of unlabeled ATP the calcium dependent level of phosphorylation declined, with a first-order rate constant of 0.12 s?1. Adding 10 mm -KCI with the unlabeled ATP increased the rate constant to 0.20 s?1, whereas adding 10 mm -NaCl did not affect it measurably. On the other hand, adding dimethyl-sulfoxide slowed the rate of loss, the constant decreasing to 0.06 s?1. Orthovanadate was a potent inhibitor of this enzyme, and inhibition with 1 μm -vanadate was increased by both KCI and dimethylsulfoxide. Properties of the enzyme are thus reminiscent of the plasma membrane (Na + K)-ATPase and the sarcoplasmic reticulum (Ca + Mg)-ATPase, most notably in the K+ stimulation of both dephosphorylation and inhibition by vanadate. 相似文献
14.
Joao B. T. Rocha Herman Wolosker †Diogo O. Souza Leopoldo de Meis 《Journal of neurochemistry》1996,66(2):772-778
Abstract: Rat brain microsomes accumulate Ca2+ at the expense of ATP hydrolysis. The rate of transport is not modulated by the monovalent cations K+, Na+, or Li+. Both the Ca2+ uptake and the Ca2+-dependent ATPase activity of microsomes are inhibited by the sulfated polysaccharides heparin, fucosylated chondroitin sulfate, and dextran sulfate. Half-maximal inhibition is observed with sulfated polysaccharide concentrations ranging from 0.5 to 8.0 µg/ml. The inhibition is antagonized by KCl and NaCl but not by LiCl. As a result, Ca2+ transport by the native vesicles, which in the absence of polysaccharides is not modulated by monovalent cations, becomes highly sensitive to these ions. Trifluoperazine has a dual effect on the Ca2+ pump of brain microsomes. At low concentrations (20–80 µM) it stimulates the rate of Ca2+ influx, and at concentrations >100 µM it inhibits both the Ca2+ uptake and the ATPase activity. The activation observed at low trifluoperazine concentrations is specific for the brain Ca2+-ATPase; for the Ca2+-ATPases found in blood platelets and in the sarcoplasmic reticulum of skeletal muscle, trifluoperazine causes only a concentration-dependent inhibition of Ca2+ uptake. Passive Ca2+ efflux from brain microsomes preloaded with Ca2+ is increased by trifluoperazine (50–150 µM), and this effect is potentiated by heparin (10 µg/ml), even in the presence of KCl. It is proposed that the Ca2+-ATPase isoform from brain microsomes is modulated differently by polysaccharides and trifluoperazine when compared with skeletal muscle and platelet isoforms. 相似文献
15.
Release of Ca2+ from the (Ca2+ + Mg2+)-ATPase into the interior of intact sarcoplasmic reticulum vesicles was measured using arsenazo III, a metallochromic indicator of Ca2+. Arsenazo III was placed inside the sarcoplasmic reticulum vesicles by making the vesicles transiently leaky with an osmotic gradient in the presence of arsenazo III. External arsenazo III was then removed by centrifugation. Addition of ATP to the (Ca2+ + Mg2+)-ATPase in the presence of Ca2+ causes the rapid phosphorylation of the enzyme at which time the bound Ca2+ becomes inaccessible to external EGTA. The release of Ca2+ from the (Ca2+ + Mg2+)-ATPase to the interior of the vesicle measured with intravesicular arsenazo III was much slower indicating that there is an occluded from the Ca2+-binding site which precedes the release of Ca2+ into the vesicle. The rate of Ca2+ accumulation by sarcoplasmic reticulum vesicles is increased by K+ (5–100 mM) and ATP (50–1000 μM) but the initial rate of Ca2+ translocation measured after the simultaneous addition of ATP and EGTA to vesicles that were preincubated in Ca2+ was not influenced by these concentrations of K+ and ATP. 相似文献
16.
The inetic properties of exchangeable Ca2+ in isolated guinea-pig heart mitochondria were studied at 25°C in the presence of 0.9 mM free Mg2+, ATP, phosphate ions and 0.4 – 0.5 μM free Ca2+ using a 45Ca2+ exchange technique. The simplest system which was found to be consistent with the data was one in which two kinetically-distinct compartments of exchangeable Ca2+ are present in the mitochondria. In the presence of 6 mM Na and at 0.4 μM free Ca2+, the fractional transfer rates for the transport of Ca2+ from these compartments were found to be 0.6 and 0.05 min?1 and the quantities of exchangeable Ca2+ 0.04 and 0.2 μmol/g wet wt heart, respectively. The amount of 45Ca2+ exchanged increased when the concentration of inorganic phosphate was increased, and decreased slightly when the concentration of free Mg2+ was increased from 1 mM to 3 mM. The flux of Ca2+ across the boundaries of both compartments was inhibited by an increase in the concentration of extramitochondrial Na+. The contribution of mitochondrial Ca2+ to compartments of kinetically-distinct exchangeable Ca2+ observed in intact cardiac muscle is briefly discussed. 相似文献
17.
J.T. OFlaherty S. Cousart C.L. Swendsen L.R. DeChatelet D.A. Bass S.H. Love C.E. McCall 《生物化学与生物物理学报:生物膜》1981,640(1):223-230
The influence of extracellular Ca2+ and Mg2+ on the transport of 2-deoxy-[3H]glucose into human polymorphonuclear neutrophils was studied. Omission of these cations from the cell suspensions had little effect on resting hexose uptake. Furthermore, the addition of the bivalent cation chelator, EDTA, depressed uptake only slightly. Similarly, neither cation was essential for the enhanced 2-deoxy-D-[3H]glucose uptake stimulated by two chemotactic factors (C5a and ) and arachidonic acid: enhanced uptake was only partially depressed by the omission of Ca2+ and Mg2+ from the suspensions and was still prominent in the presence of EDTA. Two other neutrophil stimulants, the ionophores, A23187 and ionomycin, also enhanced hexose uptake but their actions were heavily dependent upon extracellular bivalent cations and were totally abrogated by EDTA. In all instances, extracellular Ca2+, but not Mg2+, supported optimal enhanced hexose transport induced by stimuli.Activation of 2-deoxy-D-[3H]glucose uptake by each of the five stimuli was totally blocked by cytochalasin B (a blocker of carrier-mediated hexose transport) and D-glucose but not by L-glucose. The data indicate, therefore, that a variety of neutrophil stimulants activate carrier-mediated hexose transport. Although this transport can be triggered by the movement of extracellular Ca2+ into the cell (as exemplified by the action of the two ionophores), such Ca2+ movement is not required for the actions of chemotactic factors or arachidonic acid. Other mechanisms, such as a rearrangement of intracellular Ca2+, may be involved in mediating the activation of hexose transport induced by the latter stimuli. 相似文献
18.
Masato Hirata Takafumi Hamachi Eiichi Suematsu Toshitaka Koga 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1983,763(4):339-345
Effects of N-formyl chemotactic peptides on the Ca2+ influx and efflux were investigated in guinea-pig peritoneal macrophages using an isotope tracer. fMet-Leu-Phe did not enhance the influx of 45Ca2+ into macrophages, whereas it stimulated the efflux of 45Ca2+ from macrophages at concentrations ranging from 10?10 M to 10?7 M. fMet-Met-Met and fMet-Leu also stimulated the 45Ca2+ efflux, albeit at much higher concentrations, while there was no stimulation with fMet. The mitochondrial inhibitors, oligomycin and NaN3, did not modify the 45Ca2+ efflux induced by the chemoattractants, yet they did induce the release of 45Ca2+ from the mitochondria. On the other hand, higher concentrations of the calmodulin antagonists, chlorpromazine and trifluoperazine, induced the release of 45Ca2+ from the NaN3-insensitive Ca2+ store site and mimicked the enhancement of the 45Ca2+ efflux by N-formyl chemotactic peptides. Thus, N-formyl chemotactic peptides appear to increase the levels of intracellular free Ca2+ in guinea-pig peritoneal macrophages, probably by inducing the release of Ca2+ from the NaN3-insensitive Ca2+ store site. 相似文献
19.
The presence of an Na+/Ca2+ exchange system in basolateral plasma membranes from rat small intestinal epithelium has been demonstrated by studying Na+ gradient-dependent Ca2+ uptake and the inhibition of ATP-dependent Ca2+ accumulation by Na+. The presence of 75 mM Na+ in the uptake solution reduces ATP-dependent Ca2+ transport by 45%, despite the fact that Na+ does not affect Ca2+-ATPase activity. Preincubation of the membrane vesicles with ouabain or monensin reduces the Na+ inhibition of ATP-dependent Ca2+ uptake to 20%, apparently by preventing accumulation of Na+ in the vesicles realized by the Na+-pump. It was concluded that high intravesicular Na+ competes with Ca2+ for intravesicular Ca2+ binding sites. In the presence of ouabain, the inhibition of ATP-dependent Ca2+ transport shows a sigmoidal dependence on the Na+ concentration, suggesting cooperative interaction between counter transport of at least two sodium ions for one calcium ion. The apparent affinity for Na+ is between 15 and 20 mM. Uptake of Ca2+ in the absence of ATP can be enhanced by an Na+ gradient (Na+ inside > Na+ outside). This Na+ gradient-dependent Ca2+ uptake is further stimulated by an inside positive membrane potential but abolished by monensin. The apparent affinity for Ca2+ of this system is below 1 μM. In contrast to the ATP-dependent Ca2+ transport, there is no significant difference in Na+ gradient-dependent Ca2+ uptake between basolateral vesicles from duodenum, midjejunum and terminal ileum. In duodenum the activity of ATP-driven Ca2+ uptake is 5-times greater than the Na+/Ca2+ exchange capacity but in the ileum both systems are of equal potency. Furthermore, the Na+/Ca2+ exchange mechanism is not subject to regulation by 1α,25-dihydroxy vitamin D-3, since repletion of vitamin D-deficient rats with this seco-steroid hormone does not influence the Na+/Ca2+ exchange system while it doubles the ATP-driven Ca2+ pump activity. 相似文献
20.
The trimeric derivative of 16,16-dimethyl-15-dehydroprostaglandin B1 (termed tri-Calciphor), which protects tissues against ischemic damage, induced Ca2+ efflux and swelling in mitochondria in the absence of phosphate, Mg2+ and ATP. When glutamate/malate rather than succinate was the substrate, higher tri-Calciphor concentrations were required for the ionophoretic activity. Ca2+ efflux and mitochondrial swelling induced by tri-Calciphor were completely inhibited by ATP, phopsphate and Mg2+ added together, and partially inhibited with phosphate plus either ATP or Mg2+. Between 0 and 7 μM added Ca2+ and in the presence of phosphate, ATP and Mg2+, tri-Calciphor stimulated the uptake of Ca2+ by mitochondria and increased the efficiency of buffering of extramitochondrial Ca2+. Thus depending on the assay conditions, two different effects involving Ca2+ movements and mitochondria are observed with tri-Calciphor. 相似文献