共查询到20条相似文献,搜索用时 15 毫秒
1.
The release of plasma membrane ecto-enzymes by a phosphatidylinositol-specific phospholipase C from Staphylococcus aureus was investigated. There was no effect on L-leucyl-beta-naphthylamidase, alkaline phosphodeisterase I and Ca2+- or MG2+-ATPase, but substantial proportions of the alkaline phosphatase and 5-nucleotidase were released. There was no simultaneous release of phospholipid and the solubilized enzymes were not exluded from Sepharose 6-B. It was therefore concluded that release was not a secondary consequence of membrane vesiculation but occurred as a result of the disruption of specific interactions involving the phosphatidylinositol molecule. 相似文献
2.
《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1986,889(1):65-71
We investigated the role of extracellular Ca2+ in the Clostridium perfringens enterotoxin-induced alteration of the permeability of the plasma membrane. Enterotoxin released 86Rb and 51Cr from the Vero cells preloaded with the isotope. In the presence of EGTA, however, it released 86Rb but not 51Cr. The binding of enterotoxin to the cells was not influenced by Ca2+ or Mg2+. The effects of various cations on the enterotoxin-induced 51Cr release was also studied. The release depended on extracellular Ca2+ but not on Mg2+; it was inhibited by each of Zn2+, La3+ and Co2+. Zn2+ and Co2+ also inhibited 51Cr release caused by the enterotoxin previously bound to the cell membrane. In contrast, antibody against enterotoxin did not neutralize the toxin once it was bound to the Vero cells. When the cells were treated with enterotoxin, 45Ca influx occurred and reached the plateau in a few minutes, as did 86Rb release. 相似文献
3.
The influence of tetanus toxin in vitro on the release of exogenous [3H]GABA was studied with rat cerebral cortex slices. The influx, long-term accumulation and spontaneous efflux of GABA were not modified by the toxin. The release induced by high K+ (50 mM) medium from the superfused slices pretreated with the toxin was significantly inhibited in a time- and dose-dependent fashion. This release was attenuated during superfusion with Ca2+-free medium and the toxin no longer affected the remaining Ca2+-independent release. The release induced by Na+-free media did not require extracellular Ca2+ ions, and the toxin inhibited the release both with and without Ca2+. The toxin treatment had no marked influence on the ouabain (20 μM) or veratrine (25–50 μM)-induced release of GABA. The toxin treatment in vitro appears to modify some step(s) in the stimulated release of GABA without affecting its unstimulated membrane transport. Tetanus toxin may thus prove a valuable tool in studying the mechanisms of the release of GABA and possibly other inhibitory transmitters in synapses of the central nervous system. 相似文献
4.
Anderson JM 《Plant physiology》1983,71(2):333-340
The release of sucrose from leaf discs of Vicia faba L. to a bathing medium was studied for evidence of a relationship between this release and mesophyll export of photosynthate in vivo. Sucrose was released specifically over hexoses and represented over 85% of total photosynthate released. The sucrose appeared to be derived from the mesophyll tissue directly and release did not require concurrent photosynthesis. The data indicated two separate channels for sucrose release. The first was sensitive to inhibition by 1 millimolar p-chloromercuribenzenesulfonic acid and the second was promoted by lowering the Ca2+ concentration below 0.1 millimolar. Flow through both channels was about equal when tissue that had been actively photosynthesizing for several hours was used. The rate of release was not dependent on the extracellular pH, but was inhibited by 10 micromolar carbonylcyanide p-trifluromethoxyphenylhydrazone. Lowering the Ca2+ concentration below 0.1 millimolar or raising the K+ concentration above 100 millimolar stimulated sucrose release. The stimulation by high K+ was not reversed by adding Ca2+. The data supported the postulate that Ca2+ removal or K+ addition changed the permeability of the mesophyll plasma membrane to sucrose. 相似文献
5.
Mikhail V. Dubinin Victor N. Samartsev Anastasia E. Stepanova Ekaterina I. Khoroshavina Nikita V. Penkov Valery A. Yashin Vlada S. Starinets Irina B. Mikheeva Sergey V. Gudkov Konstantin N. Belosludtsev 《Journal of bioenergetics and biomembranes》2018,50(5):391-401
The paper examines membranotropic Ca2+-dependent effects of ω-hydroxypalmitic acid (HPA), a product of ω-oxidation of fatty acids, on the isolated rat liver mitochondria and artificial membrane systems (liposomes). It was established that in the presence of Ca2+, HPA induced aggregation of liver mitochondria, which was accompanied by the release of cytochrome c from the organelles. It was further demonstrated that the addition of Ca2+ to HPA-containing liposomes induced their aggregation and/or fusion. Ca2+ also caused the release of the fluorescent dye sulforhodamine B from liposomes, indicating their permeabilization. HPA was shown to induce a high-amplitude swelling of Ca2+-loaded mitochondria, to decrease their membrane potential, to induce the release of Ca2+ from the organelles and to result in the oxidation of the mitochondrial NAD(P)H pool. Those effects of HPA were not blocked by the MPT pore inhibitor CsA, but were suppressed by the mitochondrial calcium uniporter inhibitor ruthenium red. The effects of HPA were also observed when Ca2+ was replaced with Sr2+ (but not with Ba2+ or Mg2+). A supposition is made that HPA can induce a Ca2+-dependent aggregation of mitochondria, as well as Ca2+dependent CsA-insensitive permeabilization of the inner mitochondrial membrane – with the subsequent lysis of the organelles. 相似文献
6.
《Neurochemistry international》2009,54(6-8):416-423
We examined the effects of osthole and imperatorin, two active compounds of Cnidium monnieri (L.) Cusson, on the release of glutamate from rat hippocampal synaptosomes and investigated the possible mechanism. The results showed that osthole or imperatorin significantly facilitated 4-aminopridine (4-AP)-evoked glutamate release in a concentration-dependent manner. The facilitatory action of osthole or imperatorin was blocked by the vesicular transporter inhibitor bafilomycin A1, not by the glutamate transporter inhibitor l-transpyrrolidine-2,4-dicarboxylic acid (l-trans-PDC), indicating that the release facilitation by osthole or imperatorin results from a enhancement of vesicular exocytosis and not from an increase of Ca2+-independent efflux via glutamate transporter. Examination of the effect of osthole and imperatorin on cytosolic [Ca2+] revealed that the facilitation of glutamate release could be attributed to an increase in voltage-dependent Ca2+ influx. Consistent with this, ω-conotoxin MVIIC, a wide-spectrum blocker of the N- and P/Q-type Ca2+ channels, significantly suppressed the osthole or imperatorin-mediated facilitation of glutamate release, but intracellular Ca2+ release inhibitor dantrolene had no effect. Osthole or imperatorin did not alter the resting synaptosomal membrane potential or 4-AP-mediated depolarization; thus, the facilitation of 4-AP-evoked Ca2+ influx and glutamate release produced by osthole or imperatorin was not due to it decreasing synaptosomal excitability. In addition, osthole or imperatorin-mediated inhibition of 4-AP-evoked release was prevented by protein kinase C (PKC) inhibitors. Furthermore, osthole or imperatorin increased 4-AP-induced phosphorylation of PKC. Together, these results suggest that osthole or imperatorin effects a facilitation of glutamate release from nerve terminals by positively modulating N-and P/Q-type Ca2+ channel activation through a signaling cascade involving PKC. 相似文献
7.
Shigehiko Miyamoto 《生物化学与生物物理学报:生物膜》2007,1768(7):1848-1854
The LolCDE complex of Escherichia coli releases outer membrane-specific lipoproteins from the inner membrane. Lipoproteins with Asp at + 2 remain in the inner membrane since this residue functions as a LolCDE avoidance signal depending on phosphatidylethanolamine. We examined the effects of other phospholipids on lipoprotein sorting in proteoliposomes reconstituted with LolCDE and various synthetic phospholipids. The lipoprotein release and ATP hydrolysis were both low at 2 mM Mg2+ but very high at 10 mM Mg2+ in proteoliposomes containing cardiolipin alone. However, the Lol avoidance function was abolished at 10 mM Mg2+, and the release of lipoproteins with Asp at + 2 was as efficient as that of outer membrane-specific lipoproteins. The addition of phosphatidylethanolamine to cardiolipin stimulated the ATP hydrolysis and increased the Lol avoidance function of Asp at + 2 at 2 mM Mg2+. The addition of phosphatidylglycerol to cardiolipin nearly completely inhibited the release of lipoproteins with Asp at + 2 even at 10 mM Mg2+, while that of outer membrane-specific lipoproteins was not. Taken together, these results indicate that three major phospholipids of E. coli differently affect lipoprotein sorting and the activity of LolCDE. 相似文献
8.
Kenneth R. Chien S.Curtis Sherman Stewart Mittnacht John L. Farber 《Archives of biochemistry and biophysics》1980,205(2):614-622
An endogenous system in the membranes of rat liver endoplasmic reticulum is capable upon Ca2+ activation of considerable disruption of normal structure and function. Phosphatidylethanolamine (PE) and to a lesser extent phosphatidylcholine (PC) are degraded to hydrophilic products. This lipid loss is greater at an alkaline pH, preferentially utilizes millimolar Ca2+ rather than Mg2+ ions, and is inhibited by KCl. Diethyl ether has no effect on the rate of loss of PE or PC, and the Ca2+ ionophore A23187 does not lower the Ca2+ requirement. Phospholipids are most likely lost from the membranes in a two-step process. Lysophospholipids generated in the first, Ca2+-dependent step are removed by an endogenous lysophospholipase demonstrated by the hydrolysis of either added lyso PE or lysophospholipids generated from endogenous substrates by Naja naja phospholipase A2. The depletion of microsomal membrane phospholipid is accompanied by a loss of glucose 6-phosphatase and of cytochrome P-450. The latter is not associated with any change in total heme content. Polyacrylamide gel electrophoresis showed no difference between the pattern or relative amounts of solubilized membrane proteins before or after depletion of membrane phospholipid. It is concluded that activation of an endogenous phospholipase by Ca2+ can result in significant depletion of PE and PC that is accompanied by considerable disruption of membrane function. The significance of this system with respect to the maintenance of cell integrity and its possible role in cell injury are discussed. 相似文献
9.
T. Kanamori C.R. Creveling J.W. Daly 《Biochimica et Biophysica Acta (BBA)/General Subjects》1979,582(3):434-447
The boiled supernatant fraction from rat cerebrum contained factors which inhibited the basal activity of a Ca2+-dependent phosphodiesterase from rat cerebrum. Two inhibitory fractions were isolated by DEAE-cellulose or Sephadex chromatography and were deemed proteins, based on their sensitivity to trypsin digestion. The inhibitory fractions eluted from DEAE-cellulose columns prior to the Ca2+-dependent activator protein. The inhibitory factors, unlike the activator protein, were stable to heat treatment under alkaline conditions. The inhibitory factors caused both an increase in Km for cyclic GMP and a decrease in . In the presence of calcium ions and purified activator protein, the Ca2+-dependent phosphodiesterase was not inhibited by the factors, but instead was slightly stimulated. The inhibitory factors caused a slight apparent stimulation of a Ca2+-independent phosphodiesterase from rat cerebrum but this proved instead to be a nonspecific stabilizing effect which was mimicked by bovine serum albumin. After prolonged alkaline treatment, the purified activator protein caused a modest Ca2+-independent activation of Ca2+-dependent phosphodiesterase. The inhibitory factors antagonized the activation of Ca2+-dependent phosphodiesterase by alkaline treated activator protein or by lysophosphatidylcholine. The inhibitory factors had no effect on activity of trypsinized Ca2+-dependent phosphodiesterase. Of various other proteins, only casein mimicked the effects of the inhibitory factors on phosphodiesterase activity. 相似文献
10.
Treatment with chitosan of suspension-cultured Glycine max cells labeled with 45Ca2+ caused a rapid release of calcium, which was complete much earlier than the chitosan-induced leakage of intracellular electrolytes and probably reflects calcium loss primarily from the cell wall and/or plasma membrane. A linear correlation was found between calcium release from chitosan-treated whole cells or isolated cell walls and the amount of chitosan bound. Other polycations (poly-l-lysine, histone, DEAE-dextran, and protamine sulfate), low molecular weight polyamines (spermine, spermidine, and putrescine) and polyanions (polygalacturonate and poly-l-aspartate, which act as chelating agents) also released calcium from whole cells and isolated cell walls; however, only the polycations increased membrane permeability. Poly-l-lysines of differing molecular weight showed a similar ability to release calcium, but their effect on membrane permeability increased with increasing molecular weight. The results suggest that the effect of polycations on permeability is not the direct result of calcium displacement from the cell surface but is probably due to cross-linking of surface components. The order of effectiveness of inorganic cations in displacing calcium from whole cells and isolated cell walls was Ca2+, Ba2+, Sr2+ > Mg2+ > K+, Na+. 相似文献
11.
The efflux of Ca2+ from mitochondria respiring at steady state, and much of uncoupler-induced Ca2+ efflux, is shown to be a consequence of the Ca2+-induced membrane transition (the Ca2+-induced transition is the Ca2+-dependent sudden increase in the nonspecific permeability of the mitochondrial inner membrane which occurs spontaneously when mitochondria are incubated under a variety of conditions (D. R. Hunter, R. A. Haworth, and J. H. Southard, 1976, J. Biol. Chem.251, 5069–5077)). Ca2+ release from mitochondria respiring at steady state is shown to be transitional by four criteria: (1) Ca2+ release is inhibited by Mg2+, ADP, and bovine serum albumin (BSA), all inhibitors of the transition; (2) release is selective for Ca2+ over Sr2+, a selectivity also found for the transition; (3) the time course of Ca2+ release is identical to the time course of the change in the mitochondrial population from the aggregated to the orthodox configuration; and (4) from kinetics, Ca2+ release from individual mitochondria is shown to occur suddenly, following a lag period during which no release occurs. Ca2+ release induced by uncoupler is shown to be mostly by a transitional mechanism, as judged by four criteria: (1) release of Ca2+ is ruthenium red-insensitive and is an order of magnitude faster than Sr2+ release which is ruthenium red-sensitive; (2) release of Ca2+ is strongly inhibited by keeping the mitochondrial NAD+ reduced; (3) the kinetics of Ca2+ release indicates a transitional release mechanism; and (4) uncoupler addition triggers the aggregated to orthodox configurational transition which, at higher levels of Ca2+ uptake, occurs in the whole mitochondrial population at a rate equal to the rate of Ca2+ release. Na2+-induced Ca2+ release was not accompanied by a configurational change; we therefore conclude that it is not mediated by the Ca2+-induced transition. 相似文献
12.
This study hypothesized that decline in sarcoplasmic reticulum (SR) Ca2+ release and maximal SR-releasable Ca2+ contributes to decreased specific force with aging. To test it, we recorded electrically evoked maximal isometric specific force followed by 4-chloro-m-cresol (4-CmC)-evoked maximal contracture force in single intact fibers from the mouse flexor digitorum brevis muscle. Significant differences in tetanic, but not in 4-CmC-evoked, contracture forces were recorded in fibers from aging mice as compared to younger mice. Peak intracellular Ca2+ in response to 4-CmC did not differ significantly. SR Ca2+ release was recorded in whole-cell patch-clamped fibers in the linescan mode of confocal microscopy using a low-affinity Ca2+ indicator (Oregon green bapta-5N) with high-intracellular ethylene glycol-bis(α-aminoethyl ether)-N,N,N′N′-tetraacetic acid (20 mM). Maximal SR Ca2+ release, but not voltage dependence, was significantly changed in fibers from old compared to young mice. Increasing the duration of fiber depolarization did not increase the maximal rate of SR Ca2+ release in fibers from old compared to young mice. Voltage-dependent inactivation of SR Ca2+ release did not differ significantly between fibers from young and old mice. These findings indicate that alterations in excitation-contraction coupling, but not in maximal SR-releasable Ca2+, account for the age-dependent decline in intracellular Ca2+ mobilization and specific force. 相似文献
13.
Senescence-Related Changes in ATP-Dependent Uptake of Calcium into Microsomal Vesicles from Carnation Petals 总被引:3,自引:3,他引:0
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Microsomal membrane vesicles isolated from the petals of young carnation (Dianthus caryophyllus L. cv White Sim) flowers accumulate Ca2+ in the presence of ATP. The specific activity of ATP-dependent uptake is ~20 nanomoles per milligram of protein per 30 minutes. The membranes also hydrolyze ATP, but Ca2+ stimulation of ATP hydrolysis was not discernible above the high background of Ca2+-insensitive ATPase activity. The initial velocity of uptake showed a sigmoidal rise with increasing Ca2+ concentration, suggesting that Ca2+ serves both as substrate and activator for the enzyme complex mediating its uptake. The concentration of Ca2+ at half maximal velocity of uptake (S0.5) was 12.5 micromolar and the Hill coefficient (nH) was 2.5. The addition of calmodulin to membrane preparations that had been isolated in the presence of chelators did not promote ATP-dependent accumulation of Ca2+, although this may reflect the fact that the treatment with chelators did not fully remove endogenous calmodulin. Transport of Ca2+ into membrane vesicles was unaffected by 50 micromolar ruthenium red and 5 micromolar sodium azide, indicating that uptake is primarily into vesicles of non-mitochondrial origin. By subfractionating the microsomes on a linear sucrose gradient, it was established that the ATP-dependent Ca2+ transport activity comigrates with endoplasmic reticulum and plasma membrane. During post-harvest development of cut flowers, ATP-dependent uptake of Ca2+ into microsomal vesicles declined by ~70%. This occurred before the appearance of petal-inrolling and the climacteric-like rise in ethylene production, parameters that denote the onset of senescence. There were no significant changes during this period in S0.5 or nH, but Vmax for ATP-dependent Ca2+ uptake decreased by ~40%. A similar decline in ATP-dependent uptake of Ca2+ into microsomal vesicles was induced by treating young flowers with physiological levels of exogenous ethylene. 相似文献
14.
S.C. Chow L. Sisfontes M. Jondal I. Björkhem 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1991,1092(3):358-366
The effect of modifying fatty acyl composition of cellular membrane phospholipids on receptor-mediated intracellular free Ca2+ concentration ([Ca2+]i) increase was investigated in a leukemic T cell line (JURKAT). After growing for 72 h in medium supplemented with unsaturated fatty acids (UFAs) and α-tocopherol, the fatty acyl composition of membrane phospholipids in JURKAT cells was extensively modified. Each respective fatty acid supplemented in the culture medium was readily incorporated into phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine and phosphatidylcholine in the JURKAT cells. The total n ? 6 fatty acyl content was markedly reduced in phosphatidylinositol and phosphatidylcholine of cells grown in the presence of n ? 3 fatty acids (α-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid). Conversely, in the presence of n ? 6 fatty acids (linoleic acid and arachidonic acid), the total n ? 3 fatty acyl content was reduced in all the phospholipids examined. In n ? 3 and n ? 6 polyunsaturated fatty acid (PUFA) modified JURKAT cells, the total n ? 9 monounsaturated fatty acyl content in the phospholipids were markedly reduced. Changing the fatty acyl composition of membrane phospholipids in the JURKAT cells appear to have no affect on the presentation of the T cell receptor/CD3 complex or the binding of anti-CD3 antibodies (OKT3) to the CD3 complex. However, the peak increase in [Ca2+]i and the prolonged sustained phase elicited by OKT3 activation were suppressed in n ? 3 and n ? 6 PUFA but not in n ? 9 monounsaturated fatty acid modified cells. In Ca2+ free medium, OKT3-induced transient increase in [Ca2+]i, representing Ca2+ release from the inositol 1,4,5-triphosphate-sensitive Ca2+ stores, were similar in control and UFA modified cells. Using Mn2+ entry as an index of plasma membrane Ca2+ permeability, the rate of fura-2 fluorescence quenching as a result of Mn2+ influx stimulated by OKT3 in n ? 9 monounsaturated fatty acid modified cells was similar to control cells, but the rates in n ? 3 and n ? 6 PUFA modified cells were significantly lower. These results suggest that receptor-mediated Ca2+ influx in JURKAT cells is sensitive to changes in the fatty acyl composition of membrane phospholipids and n ? 9 monounsaturated fatty acids appears to be important for the maintenance of a functional Ca2+ influx mechanism. 相似文献
15.
Zuo Yu Wang Yan Fei Han Xu Huang Peng Zhao Hong Li Lu Young Chul Kim Wen Xie Xu 《Journal of biomechanics》2010,43(11):2214-2220
Membrane stretch is an important stimulus in gastrointestinal (GI) motility regulation, but the relationship between membrane stretch and the pacemaking activity of GI smooth muscle is poorly understood. We examined the effect of intestinal distension on slow waves and the effect of membrane stretch on pacemaker currents in cultured intestinal interstitial cells of Cajal (ICCs) from murine small intestine. At organ level, intestinal distension significantly increased amplitude of slow and fast waves, and enhanced frequencies of fast but not slow waves. At the cellular level, membrane stretch-induced by hyposmotic cell swelling (MSHC) depolarized membrane potential and activated large inward holding current, but suppressed amplitude of pacemaker potential or pacemaking current. External Ca2+-free solution abolished pacemaker current and blocked MSHC-induced inward holding current. However, a sustained inward holding current was activated and the amplitude of pacemaker current was increased by high ethylene glycol tetraacetic acid (EGTA) in pipette. Then MSHC also potentiated the inward holding current. MSHC significantly increased amplitude of rhythmic Ca2+ transients and basal intracellular Ca2+ concentration ([Ca2+]i). 2-APB blocked both pacemaker current and Ca2+ transients but did not alter the effect of MSHC on pacemaker current and Ca2+ transients. In contrast, ryanodine inhibited Ca2+ transients but not pacemaker current, and completely blocked MSHC-induced inward holding current and MSHC-induced increase of basal [Ca2+]i. These results suggest that intestinal distension potentiates intestinal motility by increasing the amplitude of slow waves. Membrane stretch potentiates pacemaking activity via releasing Ca2+ from calcium-induced calcium release (CICR) in cultured intestinal ICCs. 相似文献
16.
Lei Li Haowen Liu Mia Krout Janet E. Richmond Yu Wang Jihong Bai Saroja Weeratunga Brett M. Collins Donovan Ventimiglia Yi Yu Jingyao Xia Jing Tang Jie Liu Zhitao Hu 《The Journal of cell biology》2021,220(4)
Ca2+-dependent neurotransmitter release requires synaptotagmins as Ca2+ sensors to trigger synaptic vesicle (SV) exocytosis via binding of their tandem C2 domains—C2A and C2B—to Ca2+. We have previously demonstrated that SNT-1, a mouse synaptotagmin-1 (Syt1) homologue, functions as the fast Ca2+ sensor in Caenorhabditis elegans. Here, we report a new Ca2+ sensor, SNT-3, which triggers delayed Ca2+-dependent neurotransmitter release. snt-1;snt-3 double mutants abolish evoked synaptic transmission, demonstrating that C. elegans NMJs use a dual Ca2+ sensor system. SNT-3 possesses canonical aspartate residues in both C2 domains, but lacks an N-terminal transmembrane (TM) domain. Biochemical evidence demonstrates that SNT-3 binds both Ca2+ and the plasma membrane. Functional analysis shows that SNT-3 is activated when SNT-1 function is impaired, triggering SV release that is loosely coupled to Ca2+ entry. Compared with SNT-1, which is tethered to SVs, SNT-3 is not associated with SV. Eliminating the SV tethering of SNT-1 by removing the TM domain or the whole N terminus rescues fast release kinetics, demonstrating that cytoplasmic SNT-1 is still functional and triggers fast neurotransmitter release, but also exhibits decreased evoked amplitude and release probability. These results suggest that the fast and slow properties of SV release are determined by the intrinsically different C2 domains in SNT-1 and SNT-3, rather than their N-termini–mediated membrane tethering. Our findings therefore reveal a novel dual Ca2+ sensor system in C. elegans and provide significant insights into Ca2+-regulated exocytosis. 相似文献
17.
Alexey Agafonov Konstantin Belosludtsev Odile Gateau-Roesch Galina D. Mironova 《生物化学与生物物理学报:生物膜》2003,1609(2):153-160
Formation of palmitic acid/Ca2+ (PA/Ca2+) complexes was suggested to play a key role in the non-classical permeability transition in mitochondria (NCPT), which seems to be involved in the PA-induced apoptosis of cardiomyocytes. Our previous studies of complexation of free fatty acids (FFA) with Ca2+ showed that long-chain (C:16-C:22) saturated FFA had an affinity to Ca2+, which was much higher than that of other FFA and lipids. The formation of FFA/Ca2+ complexes in the black-lipid membrane (BLM) was demonstrated to induce a nonspecific ion permeability of the membrane. In the present work, we have found that binding of Ca2+ to PA incorporated into the membrane of sulforhodamine B (SRB)-loaded liposomes results in an instant release of a part of SRB, with the quantity of SRB released depending on the concentration of PA and Ca2+. The pH-optimum of this phenomenon, similar to that of PA/Ca2+ complexation, is in the alkaline range. The same picture of SRB release has been revealed for stearic, but not for linoleic acid. Along with Ca2+, some other bivalent cations (Ba2+, Sr2+, Mn2+, Ni2+, Co2+) also induce SRB release upon binding to PA-containing liposomes, while Mg2+ turns out to be relatively ineffective. As revealed by fluorescence correlation spectroscopy, the apparent size of liposomes does not alter after the addition of PA, Ca2+ or their combination. So it has been supposed that the cause of SRB release from liposomes is the formation of lipid pores. The effect of FFA/Ca2+-induced permeabilization of liposomal membranes has several analogies with NCPT, suggesting that both these phenomena are of similar nature. 相似文献
18.
Roger A. Freedman Julia A. MacLaughlin Milton M. Weiser 《Archives of biochemistry and biophysics》1981,206(2):233-241
A previous study of energy-independent in vitro Ca2+ uptake by rat intestinal epithelial membrane vesicles demonstrated that uptake by Golgi membrane vesicles was greater than that by microvillus or lateral-basal membrane vesicles, was markedly decreased in vitamin D-deficient rats, and responded specifically to 1,25-(OH)2D3 repletion (R. A. Freedman, M. M. Weiser, and K. J. Isselbacher, 1977, Proc. Nat. Acad. Sci. USA74, 3612–3616; J. A. MacLaughlin, M. M. Weiser, and R. A. Freedman, 1980, Gastroenterology78, 325–332). In the present study, properties of Ca2+ uptake and release by intestinal Golgi membrane vesicles have been investigated. The initial rate of uptake was found to be saturable, suggesting carrier-mediated uptake. Uptake was markedly inhibited by Mg2+ and Sr2+, but not by Na+ or K+. Lowering the external [H+] or raising the internal [H+] resulted in enhancement of the initial rate of uptake; the intial rate was found to correlate with the internal-to-external [H+] gradient. The initial rate of uptake could be enhanced by preloading the vesicles with MgCl2 or SrCl2 but not CaCl2, NaCl, or KCl. Vesicles preloaded with K2SO4 failed to show enhanced uptake in the presence of valinomycin, suggesting that enhancement in uptake by vesicles preloaded with MgCl2 was not due to transmembrane potentials. The internal volume of the Golgi membrane vesicles was determined and found to be 9 μl/mg protein; this volume could accomodate less than 1% of the Ca2+ uptake maintained at equilibrium. Therefore, the remainder of the Ca2+ taken up was presumably bound to the Golgi membranes. A dissociation constant of 3.8 × 10?6m was found for this binding. The bound Ca2+ could be rapidly released by external Mg2+ or Sr2+, but not Ca2+, Na+, or K+. Release of bound Ca2+ could also be induced by raising the [H+] of the external medium. Failure of external Ca2+ to release bound Ca2+ suggested that the release induced by external Mg2+, Sr2+, or H+ was not due to competitive displacement of Ca2+ from its binding sites. These results indicated that Ca2+ uptake by intestinal Golgi membrane vesicles consists of carrier-mediated transport followed by binding of Ca2+ to the vesicle. The effects of H+, Mg2+, and Sr2+ on Ca2+ uptake and release suggest the existence of cation countertransport in the Golgi membrane vesicles. 相似文献
19.
The mitochondrial electron transport chain is the major source of reactive oxygen species (ROS) during cardiac ischemia. Several mechanisms modulate ROS production; one is mitochondrial Ca2+ uptake. Here we sought to elucidate the effects of extramitochondrial Ca2+ (e[Ca2+]) on ROS production (measured as H2O2 release) from complexes I and III. Mitochondria isolated from guinea pig hearts were preincubated with increasing concentrations of CaCl2 and then energized with the complex I substrate Na+ pyruvate or the complex II substrate Na+ succinate. Mitochondrial H2O2 release rates were assessed after giving either rotenone or antimycin A to inhibit complex I or III, respectively. After pyruvate, mitochondria maintained a fully polarized membrane potential (ΔΨ; assessed using rhodamine 123) and were able to generate NADH (assessed using autofluorescence) even with excess e[Ca2+] (assessed using CaGreen-5N), whereas they remained partially depolarized and did not generate NADH after succinate. This partial ΔΨ depolarization with succinate was accompanied by a large release in H2O2 (assessed using Amplex red/horseradish peroxidase) with later addition of antimycin A. In the presence of excess e[Ca2+], adding cyclosporin A to inhibit mitochondrial permeability transition pore opening restored ΔΨ and significantly decreased antimycin A-induced H2O2 release. Succinate accumulates during ischemia to become the major substrate utilized by cardiac mitochondria. The inability of mitochondria to maintain a fully polarized ΔΨ under excess e[Ca2+] when succinate, but not pyruvate, is the substrate may indicate a permeabilization of the mitochondrial membrane, which enhances H2O2 emission from complex III during ischemia. 相似文献
20.
《生物化学与生物物理学报:生物膜》1985,812(2):553-560
During centrifugation of Dictyostelium membranes on sucrose and metrizamide gradients, an ATPase activity resistant to azide and molybdate but sensitive to diethylstilbestrol was found to copurify with the plasma membrane markers alkaline phosphatase and 125I in cells surface-labelled by lactoperoxidase catalyzed iodination. This ATPase was enriched 50-fold in purified plasma membranes and could be separated from the mitochondrial ATPase on metrizamide gradients. The plasma membrane ATPase is very specific for ATP as substrate and Mg2+ as essential cofactor. Its pH optimum is 6.5 and it is inhibited by dicyclohexylcarbodiimide, diethylstilbestrol, vanadate, mercurials and Cu2+, but not by ouabain, molybdate, azide or oligomycin. It was not specifically affected by either monovalent cations or anions. These results suggest that the plasma membranes of Dictyostelium contain an ATPase similar to the proton-pumping ATPases recently identified in fungal and plant plasma membranes (Serrano, R. (1984) Curr. Top. Cell. Regul. 23, 87–126). 相似文献