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1.
Calcium uptake by rabbit skeletal muscle sarcoplasmic reticulum vesicles in phosphate-containing media exhibits time-dependent changes that arise from changing rates of calcium influx and efflux. The monovalent cation ionophore gramicidin, added before the start of the calcium uptake reaction, delayed the spontaneous calcium release that normally occurred after approx. 6 min in such reactions; the rate of calcium efflux was inhibited while calcium influx was little affected. Under these conditions, Ca2+-activated ATPase activity could remain unaltered. Gramicidin stimulated calcium uptake irrespective of the presence of a K+ gradient across the vesicle membrane. Valinomycin stimulated calcium uptake in a manner similar to that for gramicidin even in an NaCl-containing medium lacking potassium. Thus, dissipation of a transmembrane K+ gradient is unlikely to account for the effects of these ionophores on the spontaneous changes in calcium flux rates. Addition of gramicidin to partially calcium-filled vesicles inhibited the phase of spontaneous calcium reuptake because both calcium influx and efflux wre inhibited. Addition of gramicidin to partially calcium-filled vesicles in the presence of a water-soluble protein, such as bovine serum albumin, creatine kinase or pyruvate kinase, markedly stimulated calcium uptake. This stimulatory effect was due primarily to inhibition of calcium efflux, calcium influx being minimally influenced by the ionophore. After cleavage of the 100,000 dalton ATPase to 50,000 dalton fragments, which was not associated with changes in Ca2+-activated ATPase activity or initial calcium uptake rate, gramicidin increased rather than decreased calcium content when added to vesicles after the initial maximum in calcium content. Thus, the ability of monovalent cation ionophores to block calcium efflux from calcium-filled vesicles may reflect their interaction with a portion of the Ca2+-activated ATPase protein. 相似文献
2.
Unfractionated and low buoyant density sarcoplasmic reticulum vesicles released calcium spontaneously after ATP- or acetyl phosphate-supported calcium uptake when internal Ca 2+ was stabilized by the use of 50 mM phosphate as calcium-precipitating anion. This spontaneous calcium release could not be attributed to falling Ca 2+ concentration outside the vesicles (Ca 02+), substrate depletion, ADP accumulation, nonspecific membrane deterioration or the attainment of a high vesicular calcium content. Instead, spontaneous calcium release was directly proportional to Ca 02+ at the time that calcium content was maximal. A causal relationship between high Ca 02+ and spontaneous calcium release was suggested by the finding that elevation of Ca 02+ from less than 1 μM to 3–5 μM increased the rate and extent of calcium release.The spontaneous calcium release was due both to acceleration of calcium efflux and slowing of calcium influx that was not accompanied by a significant change in the rate of ATP hydrolysis. Neither reversal of the transmembrane KCl gradient nor incubation with cation and proton ionophores abolished the spontaneous calcium release. The persistence of calcium release under conditions where the membrane was permeable to both anions and cations makes it unlikely that this phenomenon is due to a changing transmembrane potential. 相似文献
3.
The efflux of K + and Na + from sea urchin eggs during Ca 2+ ionophore A23187-induced parthenogenesis was studied in a K + and Na +-free artificial seawater using extracellular ion-specific electrodes. We have probed this model system with monovalent cation-specific ionophores to determine if they affect K + efflux in the unfertilized egg and whether any changes in ionophore sensitivity are observed during egg activation. In 500 mM choline chloride, 10 mM CaCl 2, 50 mM MgCl 2, 10 mM Tris-Cl pH 8.0, A23187 induced a rapid efflux of K + and Na + from the eggs after a short lag time (10–15 seconds). After the burst, the rate of K + efflux remained higher than the pre-activation rate, but was lower than during the burst phase, while the rate of Na + efflux became nearly zero. Monovalent cation-specific ionophores (valinomycin, gramicidin and nigericin) had no effect on K + efflux from the unfertilized eggs in our model system. However, once the egg was activated by A23187, each of the above ionophores caused a prolongation of the burst phase for many minutes. These results show that the unfertilized egg plasma membrane (using our artificial conditions) is not susceptible to the monovalent cation-specific antibiotics and suggest that either the inserted cortical granule membrane or the developing fertilization envelope interacts with these ionophores to cause the change in rate-limiting step for K + efflux observed egg activation. 相似文献
4.
Amylase released from mouse parotid fragments by the β-adrenergic agonist, isoproterenol, was associated with l) enhanced 45Ca ++ efflux and 2) a dependence on the extracellular Na + concentration. Monensin, a sodium ionophore, mimicked the effects of isoproterenol on 45Ca ++ efflux. In the absence of extracellular sodium isoproterenol and monensin failed to significantly release 45Ca ++. Complete inhibition of isoproterenol stimulated amylase release occurred when 75 per cent or greater of the extracellular Na + was replaced by sucrose; carbachol stimulated amylase release was not affected. Tetracaine (0.2 mM to 1.0 mM) inhibited both isoproterenol and carbachol stimulated amylase release and inhibited the 45Ca ++ uptake induced by carbachol. Monensin, a sodium ionophore, mimicked the effects of isoproterenol on amylase release; this effect was significantly reduced in the absence of extracellular Na +. It is proposed that a primary step in the release of amylase form mouse parotid gland in response to β-adrenergic stimulation is an increased influx of Na + followed by release of intracellularly stored calcium. 相似文献
5.
Epinephrine stimulated adenylate cyclase in turkey erythrocyte ghosts is inhibited by calcium. The inhibition of adenylate cyclase is not apparent when intact erythrocytes are incubated with calcium and epinephrine. However, in the presence of the specific cation ionophore A 23187 and 5 mm Ca 2+, a 90% inhibition of epinephrine stimulated 3′,5′-adenosine monophosphate formation is found. The effect of catecholamines on calcium transport in the intact turkey erythrocyte was studied. Epinephrine causes a small but significant increase in Ca 2+ efflux. This effect is inhibited by propranolol. No effect of epinephrine on Ca 2+ uptake was observed. However, a 22% increase in Ca 2+ uptake in the presence of propranolol could be detected. The propranolol effect was found to possess high statistical significance ( p < .001). The absence of an epinephrine effect on influx probably reflects the presence of endogenous catecholamines in the control samples.It is proposed that the activation of adenylate cyclase by catecholamines occurs in two phases. The first phase is the increase of net Ca 2+ efflux from a crucial Ca 2+ pool, thus removing Ca 2+ from its inhibitory sites on the adenylate cyclase complex. The second phase is the activation of the deinhibited adenylate cyclase by the hormone. 相似文献
6.
Transport of Ca 2+ in membrane vesicles of the cyanobacterium Anabaena variabilis has been investigated. The light membranes previously shown to carry a Mg 2+-dependent, Ca 2+-stimulated ATPase (Lockau, W. and Pfeffer, S. (1982) Z. Naturforsch. 37C, 658–664) accumulate Ca 2+ upon addition of ATP, whereas the (heavier) thylakoids do not. A stoichiometry of 0.3 Ca 2+ taken up per ATP hydrolyzed has been determined from initial rates, which is considered to be an underestimation of the true stoichiometry of the pump. Calcium transport and Ca 2+-stimulated ATPase activity are both sensitive to Na 3VO 4 (an inhibitor of ATPases forming a phosphorylated intermediate), show the same pH optimum and a comparable dependence on ATP concentration. Calcium transport is also supported by nucleoside triphosphates other than ATP, although at lower rates. Accumulation of calcium is abolished by an ionophore of divalent cations, ionophore A23187, but is resistant to ionophores of monovalent cations and to the inhibitor of F 1-F 0-type ATPases, N, N′-dicyclohexylcarbodiimide. It is concluded that the ATPase is a primary calcium pump. 相似文献
7.
The ATP dependent Ca 2+ uptake of platelet vesicles was inhibited by the two hydrophobic drugs trifluoperazine (TFP) and propranolol (PROP). Inhibition was significantly lowered when Pi was used instead of oxalate as a precipitant agent. When the ATPase ligands substrate (Mg 2+ and Pi) were absent of the efflux medium, a slow release of Ca 2+ which did not couple with ATP synthesis (passive Ca 2+ efflux) was observed. Both, TFP and PROP enhanced the passive Ca 2+ efflux. This enhanced efflux was partially inhibited only when Mg 2+ and Pi were added together to the efflux reaction media, but it was not affected by spermidine, ruthenium red or thapsigargin (TG). The Ca 2+ ionophores A23187 and ionomycin, also enhanced passive Ca 2+ efflux. However, in this case, Ca 2+ efflux was inhibited just by inclusion of Mg 2+ to the medium. Ca 2+ efflux promoted by Triton X-100 was not affected by either Mg 2+ or Pi, included together or separately into the efflux medium. The ATP Pi measured in the presence of Triton X-100 and millimolar Ca 2+ concentrations was inhibited by both TFP and PROP, but not by Ca 2+ ionophores up to 4 M. The data suggest that the observed enhancement of passive Ca 2+ efflux promoted by TFP and PROP could be attributed to a direct effect of these drugs over the platelet Ca 2+ pump isoforms (Sarco Endoplasmic Reticulum Calcium ATPase, SERCA 2b and SERCA 3) themselves, as it was reported for the sarcoplasmic reticulum Ca 2+ ATPase (SERCA 1). 相似文献
8.
Abstract: Activation of the Ca 2+/Mg 2+ ATPase associated with highly purified Torpedo synaptic vesicles results in 45Ca 2+ uptake. The accumulated 45Ca 2+ is released by hypoosmotic buffer and by the Ca 2+ ionophore A23187. Density-gradient centrifugation and permeation chromatography reveal that vesicular acetylcholine and the membrane-bound 45Ca 2+ co-migrate, thus implying that 45Ca 2+ is transported into cholinergic vesicles. ATP-dependent 45Ca 2+ uptake follows saturation kinetics, with KmCa2+= 50 μM, KmATP= 5 μM, and V max= 3 ± 0.3 nmol Ca 2+/mg protein/min. Treatment of the vesicles with mersalyl, dicyclohexyl-carbodiimide, and quercetin leads to inactivation of the Ca 2+/Mg 2+ ATPase and to comparable inhibition of 45Ca 2+ transport. Ruthenium red and ouabain have no effect on either of these activities. Nigericin in the presence of external K + is a potent inhibitor of 45Ca 2+ translocation, whereas gramicidin activates transport. The proton translocator carbonylcyanide p-trifluoromethoxy-phenylhydrazone (FCCP) and FCCP + the ionophore valinomycin partially inhibit 45Ca 2+ transport. By contrast, the above ionophores do not affect Ca 2+/Mg 2+ ATPase activity. Tentative mechanisms for ATP-dependent Ca 2+ transport into cholinergic synaptic vesicles and the physiological significance of this process are discussed. 相似文献
9.
Sealed microsomal vesicles were prepared from corn ( Zea mays, Crow Single Cross Hybrid WF9-Mo17) roots by centrifugation of a 10,000 to 80,000 g microsomal fraction onto a 10% dextran T-70 cushion. The Mg 2+-ATPase activity of the sealed vesicles was stimulated by Cl − and NH 4+ and by ionophores and protonophores such as 2 micromolar gramicidin or 10 micromolar carbonyl cyanide p-trifluoromethoxyphenyl hydrazone (FCCP). The ionophore-stimulated ATPase activity had a broad pH optimum with a maximum at pH 6.5. The ATPase was inhibited by NO 3−, was insensitive to K +, and was not inhibited by 100 micromolar vanadate or by 1 millimolar azide. Quenching of quinacrine fluorescence was used to measure ATP-dependent acidification of the intravesicular volume. Quenching required Mg2+, was stimulated by Cl−, inhibited by NO3−, was insensitive to monovalent cations, was unaffected by 200 micromolar vanadate, and was abolished by 2 micromolar gramicidin or 10 micromolar FCCP. Activity was highly specific for ATP. The ionophore-stimulated ATPase and ATP-dependent fluorescence quench both required a divalent cation (Mg2+ ≥ Mn2+ > Co2+) and were inhibited by high concentrations of Ca2+. The similarity of the ionophore-stimulated ATPase and quinacrine quench and the responses of the two to ions suggest that both represent the activity of the same ATP-dependent proton pump. The characteristics of the proton-translocating ATPase differed from those of the mitochondrial F1F0-ATPase and from those of the K+-stimulated ATPase of corn root plasma membranes, and resembled those of the tonoplast ATPase. 相似文献
10.
The mechanism of sucrose transport into the vacuole of root parenchyma cells of sugar beet was investigated using discs of intact tissue. Active sucrose uptake was evident only at the tonoplast. Sucrose caused a transient 8.3 millivolts depolarization of the membrane potential, suggesting an ion co-transport mechanism. Sucrose also stimulated net proton efflux. Active (net) uptake of sucrose was strongly affected by factors that influence the alkali cation and proton gradients across biological membranes. Alkali cations (Na + and K +) at 95 millimolar activity stimulated active uptake of sucrose 2.1- to 4-fold, whereas membrane-permeating anions inhibited active sucrose uptake. The pH optima for uptake was between 6.5 and 7.0, pH values slightly higher than those of the vacuole. The ionophores valinomycin, gramicidin D, and carbonyl cyanide m-chlorophenylhydrazone at 10 micromolar concentrations strongly inhibited active sucrose uptake. These data are consistent with the hypothesis that an alkali cation influx/proton efflux reaction is coupled to the active uptake of sucrose into the vacuole of parenchyma cells in the root sink of sugar beets. 相似文献
11.
The uptake of proline and glutamine by cytochrome-deficient cells of Escherichia coli SASX76 grown aerobically on glucose or anaerobically on pyruvate was stimulated by these two substrates. Pyruvate could not stimulate transport in the glucose-grown cells. Uptake of these amino acids energized by glucose was inhibited by inhibitors of the Ca 2+, Mg 2+-stimulated ATPase such as DCCD, pyrophosphate, and azide, and by the uncouplers CCCP and 2,4-dinitrophenol. Glycerol (or glycerol 3-phosphate) in the presence of fumarate stimulated the transport of proline and glutamine under anaerobic conditions in cytochrome-deficient cells but not in membrane vesicles prepared from these cells although glycerol 3-phosphate-fumarate oxidoreductase activity could be demonstrated in the vesicle preparation. In contrast, in vesicles prepared from cytochrome-containing cells of E. coli SASX76 amino acid transport was energized under anaerobic conditions by this system. Inhibitors of the Ca 2+, Mg 2+-activated ATPase and uncoupling agents inhibited the uptake of proline and glutamine in cytochrome-deficient cells dependent on the glycerol-fumarate oxidoreductase system. Ferricyanide could replace fumarate as an electron acceptor to permit transport of phenylalanine in cytochrome-deficient or cytochrome- containing cells under anaerobic conditions. It is concluded that in cytochrome-deficient cells using glucose, pyruvate, or glycerol in the presence of fumarate, transport of both proline and glutamine under anaerobic conditions is energized by ATP through the Ca 2+, Mg 2+-activated ATPase. In cytochrome-containing cells under anaerobic conditions electron transfer between glycerol and fumarate can also drive transport of these amino acids. 相似文献
12.
Summary The effects of calcium ionophores on cellular calcium metabolism were studied in cultured kidney cells, in cells freshly isolated from rat kidney, and in liver and kidney slices. In isolated cells, these ionophores decreased the total cellular Ca content and the mitochondrial Ca. 45Ca efflux from prelabelled cells was also stimulated even in the absence of extracellular Ca. In slices, the ionophore A23187 increased the total slice Ca and the uptake of 45Ca. However, the mitochondria isolated from these slices treated with the ionophore had a lower total Ca and a depressed relative radioactivity. These results suggest that the increased cytosolic Ca produced by Ca ionophores may be due to mobilization of intracellular Ca stores rather than to a net shift of Ca from the extracellular fluids to the cell. 相似文献
13.
The divalent cation selective ionophores A23187 and ionomycin were compared for their effects on the Ca 2+ contents, nucleotide contents, and protein synthetic rates of several types of cultured cells. Both ionophores reduced amino acid incorporation by approximately 85% at low concentrations (50–300 nmol/L) in cultured mammalian cells without reducing ATP or GTP contents. At these concentrations A23187 and ionomycin each promoted substantial Ca 2+ efflux, whereas at higher concentrations a large influx of the cation was observed. Ca 2+ influx occurred at lower ionophore concentrations and to greater extents in C6 glioma and P3X63Ag8 myeloma than in GH 3 pituitary cells. The ATP and GTP contents of the cells and their ability to adhere to growth surfaces declined sharply at ionophore concentrations producing increased Ca 2+ influx. Prominent reductions of nucleotide contents occurred in EGTA-containing media that were further accentuated by extracellular Ca 2+. Ionomycin produced more Ca 2+ influx and nucleotide decline than comparable concentrations of A23187. The inhibition of amino acid incorporation and mobilization of cell-associated Ca 2+ by ionomycin were readily reversed in GH 3 cells by fatty acid-free bovine serum albumin, whereas the effects of A23187 were only partially reversed. Amino acid incorporation was further suppressed by ionophore concentrations depleting nucleotide contents. Mitochondrial uncouplers potentiated Ca 2+ accumulation in response to both ionophores. At cytotoxic concentrations Lubrol PX abolished protein synthesis but did not cause Ca 2+ influx. Nucleotide depletion at high ionophore concentrations is proposed to result from increased plasmalemmal Ca 2+-ATPase activity and dissipation of mitochondrial proton gradients and to cause intracellular Ca 2+ accumulation. Increased Ca 2+ contents in response to Ca 2+ ionophores are proposed as an indicator of ionophore-induced cytotoxicity.Abbreviations BSA
bovine serum albumin
- EGTA
[ethylenebis(oxyethylenenitrilo)]tetraacetic acid
- PKR
double-stranded RNA-regulated protein kinase
- ER
endoplasmic reticulum
- eIF
eukaryotic initiation factor 相似文献
14.
- 1.1. Nereis pharangeal visceral muscle is composed of obliquely striated fibres with low mitochondrial density and moderately developed sarcoplasmic reticulum.
- 2.2. Isolated mitochondria and sarcoplasmic reticulum showed moderate passive calcium binding but only low ATP-promoted calcium binding which was inhibited by caffeine.
- 3.3. Whole fibres preloaded with Ca45 showed a two compartment efflux. The slow, presumably intracellular, compartment accounted for only 10% of total Ca45 activity.
- 4.4. Both acetylcholine and high KCl treatments stimulated calcium influx, causing contractures while calcium-free and EGTA treatments inhibited both these contractures and normal spontaneous contractions.
- 5.5. Lanthanum inhibited normal contractility and KCl contractures. Lanthanum also inhibited Ca45 influx but was without effect on Ca45 efflux.
- 6.6. It is concluded that there is little calcium storage capacity in these visceral muscle fibres and that normal contractions are strongly dependent upon extracellular calcium influx.
相似文献
15.
The effects of quinacrine on depolarization-induced [ 3H]acetylcholine (ACh) release and 45Ca 2+ influx were examined in rat brain cortical synaptosomes. Quinacrine significantly reduced the stimulated release of [ 3H]ACh by high K + and veratridine without affecting the spontaneous efflux from the preloaded synaptosomes. Quinacrine had no effect on ionophore A23187-induced release of [ 3H]ACh from the synaptosomes. Quinacrine (100 μ M) markedly diminished the stimulated Ca 2+ influx by veratridine and high K + but not that by “Na +-free.” Trifluoperazine, a potent calmodulin antagonist, inhibited both Ca 2+ influx and ACh release induced by the depolarizing agents. Inhibitory potencies of the two drugs on ACh release and Ca 2+ influx were compared with the antagonism of calmodulin by two drugs, suggesting that the inhibition of depolarization-induced Ca 2+ influx and ACh release by these drugs could not be explained by the antagonism of calmodulin. 相似文献
16.
Abstract: Rat brain microsomes accumulate Ca 2+ at the expense of ATP hydrolysis. The rate of transport is not modulated by the monovalent cations K +, Na +, or Li +. Both the Ca 2+ uptake and the Ca 2+-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, Ca 2+ 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 Ca 2+ pump of brain microsomes. At low concentrations (20–80 µ M) it stimulates the rate of Ca 2+ influx, and at concentrations >100 µ M it inhibits both the Ca 2+ uptake and the ATPase activity. The activation observed at low trifluoperazine concentrations is specific for the brain Ca 2+-ATPase; for the Ca 2+-ATPases found in blood platelets and in the sarcoplasmic reticulum of skeletal muscle, trifluoperazine causes only a concentration-dependent inhibition of Ca 2+ uptake. Passive Ca 2+ efflux from brain microsomes preloaded with Ca 2+ is increased by trifluoperazine (50–150 µ M), and this effect is potentiated by heparin (10 µg/ml), even in the presence of KCl. It is proposed that the Ca 2+-ATPase isoform from brain microsomes is modulated differently by polysaccharides and trifluoperazine when compared with skeletal muscle and platelet isoforms. 相似文献
17.
Ca 2+ 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 CaCl 2, 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, Ca 2+ uptake of sarcoplasmic reticulum vesicles reached a plateau of about 100 nmol/mg. In modified medium, after this phase of Ca 2+ uptake, a second phase of Ca 2+ accumulation was initiated and reached a plateau of about 300 nmol/mg. The second phase of Ca 2+ 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 Ca 2+ uptake in modified medium but not in normal medium could not be explained by different phosphate accumulation in the two media. Unidirectional Ca 2+ influx of sarcoplasmic reticulum near steady state of Ca 2+ uptake was measured by pulse labeling with 45Ca 2+. The Ca 2+ efflux rate was then determined by subtracting the net uptake from the influx rate. At the first plateau of Ca 2+ uptake in normal medium, Ca 2+ influx was balanced by Ca 2+ 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 Ca 2+ exchange rate at the first plateau of Ca 2+ uptake was about half of that in normal medium. When the second phase of Ca 2+ 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 Ca 2+ 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 Ca 2+ uptake was also observed. These data suggest that the Ca 2+ load attained by sarcoplasmic reticulum vesicles during active transport is modulated by ADP accumulated from ATP hydrolysis. ADP probably exerts its effect by facilitating Ca 2+ efflux, which subsequently stimulates Ca 2+ exchange. 相似文献
18.
Aggregating Dictyostelium cells release protons when stimulated with cAMP. To find out whether the protons are generated by acidic vesicles or in the
cytosol, we permeabilized the cells and found that this did not alter the cAMP-response. Proton efflux in intact cells was
inhibited by preincubation with the V-type H + ATPase inhibitor concanamycin A and with the plasma membrane H + ATPase blocker miconazole. Surprisingly, miconazole also inhibited efflux in permeabilized cells, indicating that this type
of H + ATPase is present on intracellular vesicles as well. Vesicular acidification was inhibited by miconazole and by concanamycin
A, suggesting that the acidic vesicles contain both V-type and P-type H + ATPases. Moreover, concanamycin A and miconazole acted in concert, both in intact cells and in vesicles. The mechanism of
cAMP-induced Ca 2+-fluxes involves phospholipase A 2 activity. Fatty acids circumvent the plasma membrane and stimulate vesicular Ca 2+-efflux. Here we show that arachidonic acid elicited H +-efflux not only from intact cells but also from acidic vesicles. The target of regulation by arachidonic acid seemed to be
the vesicular Ca 2+-relase channel. 相似文献
19.
Fenarimol is a fungicide classified as a sterol biosynthesis inhibitor (SBI). Its passive influx in mycelium of wild-type and SBI-resistant strains of Aspergillus nidulans is counteracted by an energy-dependent efflux. Sodium orthovanadate, the ionophores nigericin and valinomycin, and the cationic agents Cu 2+, cetylpyridinium bromide, and dodine inhibit the energy-dependent efflux of fenarimol and thus allow this fungicide to accumulate in mycelium of both wild-type and SBI-resistant strains. The ionophore gramicidin and anionic and neutral detergents had the opposite effect. It is suggested that fenarimol efflux is mediated by the electrochemical proton gradient across the fungal plasma membrane. 相似文献
20.
Summary The intestinal secretagogues ricinoleate and deoxycholate have been tested for a capacity to form complexes with Ca 2+ ions and to affect the passive equilibration of Ca 2+ ions across the jejunal brush border membrane. Both of these agents formed butanol-soluble Ca 2+ complexes in a model phase distribution system. They also promote the passive uptake and efflux of Ca 2+ across brush border vesicles in a concentrationdependent manner. The levels of ricinoleate and deoxycholate that increase the rate of transvesicular Ca 2+ movement are in the 100 to 300 m range. Concentrations as high as 1.0 mm had no significant detergent effects in vesicles as measured by release of entrapped sorbitol. The kinetics of Ca 2+ uptake and efflux are similar in brush border vesicles treated with A23187, ricinoleate, or deoxycholate. The influx rates observed in this study were high enough to cause the collapse of a Ca 2+ gradient, which had been generated by Ca-Mg ATPase enzyme activity in the brush border membrane. Ricinoleate did not affect Ca-Mg ATPase activity at concentrations used in this study, but deoxycholate was inhibitory, indicating two potential modes for elevation of intracellular Ca 2+ content by deoxycholate. When compared with the effects of the Ca 2+ ionophore, A23187, it appears that both ricinoleate and deoxycholate could have significant intestinal secretory activity due to this Ca 2+ ionophore property. It is also noteworthy that, at least in this model system, potential secretory effects are expressed at concentrations significantly below levels that have been associated with detergent effects or altered epithelial morphology. 相似文献
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