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1.
Summary Ethacrynic acid greatly inhibited net transport of ions and aerobic, energyconserving metabolism in slices of avian salt gland, rat liver, and rat and guinea-pig kidney cortex. The effects of increasing concentrations of ethacrynic acid on the transport of Na+, K+ and Cl ran closely parallel to its effects on tissue ATP levels and respiration. The concentration needed for maximal inhibition of transport reduced ATP levels by 80–90%. Respiration was reduced by 80–90% in salt gland and kidney cortex, and by a maximum of 30% in liver slices. The effects of low concentrations of ethacrynic acid required time to become fully manifest in some tissues, and the development of transport inhibition followed a similar course to decline of respiration and ATP levels. Ca2+ extrusion by liver cells was inhibited by ethacrynic acid. The concentration dependence of the inhibition was similar to that shown by the other transport systems inhibited. There was no distinction evident between the sensitivity of Na+ extrusion and of K+ accumulation to the diuretic. Lactate production increased as respiration decreased in the presence of increasing concentrations of ethacrynic acid. We conclude that ethacrynic acid acted primarily as an inhibitor of mitochondrial respiration and ATP synthesis in the tissue slices, and that inhibition of ion transport was a nonspecific consequence of the failure of the energy supply.  相似文献   

2.
Slicing and incubating rat liver caused a rapid Ca2+-independent exchange of K+ for Na+, followed by a Ca2+-dependent recovery. Freshly cut slices washed for 10 min in a Ca2+ medium containing equal concentrations of Na+ and K+ showed little replacement of K+ by Na+ during subsequent incubation in a normal medium. Changes in medium Ca2+ caused immediate changes in slice Na+ and K+, before any substantial change in slice Ca2+ and without altering gradients responsible for passive transfers of Na+ and K+. Ca2+ did not influence an ouabain-sensitive Na+ pump. It also appeared unlikely that Ca2+ was required for an ouabain-insensitive Na+ pump or for maintenance of intracellular structures concerned with K+ sorption, even if these mechanisms existed in the slices. Instead Ca2+ seemed to maintain the cell membrane relatively impermeable to Na+ and K+. An ouabain-sensitive Na+ pump not normally dependent on oxygen supply to the cells appeared to alter its activity according to the work required of it. Control of slice water content could not be attributed to the activity of this pump.  相似文献   

3.
In goose salt gland slices incubated in bicarbonate-buffered medium which contained 170 mEq of Na+/liter, net total tissue Na+, expressed as milliequivalents per kilogram, was, in the presence of either acetylcholine (plus eserine) or ouabain, significantly higher than that of the bathing fluid. Acetylcholine caused an increase in the tissue Na+ content as compared with untreated slices; there was an approximately equivalent decrease in K+ and a significant decrease in Cl-. The calculated net intracellular concentrations of Na+, expressed as milliequivalents per liter of intracellular water, in unstimulated, acetylcholine-stimulated, and ouabain-treated slices were 2.1, 3.1, and 2.7 times higher, respectively, than the concentration of Na+ in the bathing fluid. The net intracellular concentration of Na+, expressed as milliequivalents per liter of intracellular water, in slices incubated in the presence of acetylcholine was 531 mEq/liter; this is approximately the same as the concentration of Na+ in the secreted fluid of the goose salt gland (515 mEq/liter). The results indicate that the main concentration gradient for Na+ could be established across the basal membrane. The data do not indicate whether this involves active transport of Na+ per se. A second stage which might involve Na-K ATPase activity at the luminal membrane is discussed. The sum of the total tissue Na+ and K+ was approximately 250 mEq/kg, whereas the Cl- content was only approximately 130 mEq/kg.  相似文献   

4.
Summary To study the physiological role of the bidirectionally operating, furosemide-sensitive Na+/K+ transport system of human erythrocytes, the effect of furosemide on red cell cation and hemoglobin content was determined in cells incubated for 24 hr with ouabain in 145mm NaCl media containing 0 to 10mm K+ or Rb+. In pure Na+ media, furosemide accelerated cell Na+ gain and retarded cellular K+ loss. External K+ (5mm) had an effect similar to furosemide and markedly reduced the action of the drug on cellular cation content. External Rb+ accelerated the Na+ gain like K+, but did not affect the K+ retention induced by furosemide. The data are interpreted to indicate that the furosemide-sensitive Na+/K+ transport system of human erythrocytes mediates an equimolar extrusion of Na+ and K+ in Na+ media (Na+/K+ cotransport), a 1:1 K+/K+ (K+/Rb+) and Na+/Na+ exchange progressively appearing upon increasing external K+ (Rb+) concentrations to 5mm. The effect of furosemide (or external K+/Rb+) on cation contents was associated with a prevention of the cell shrinkage seen in pure Na+ media, or with a cell swelling, indicating that the furosemide-sensitive Na+/K+ transport system is involved in the control of cell volume of human erythrocytes. The action of furosemide on cellular volume and cation content tended to disappear at 5mm external K+ or Rb+. Thein vivo red cell K+ content was negatively correlated to the rate of furosemide-sensitive K+ (Rb+) uptake, and a positive correlation was seen between mean cellular hemoglobin content and furosemide-sensitive transport activity. The transport system possibly functions as a K+ and waterextruding mechanism under physiological conditiosin vivo. The red cell Na+ content showed no correlation to the activity of the furosemide-sensitive transport system.  相似文献   

5.
G.D.V. Van Rossum 《BBA》1976,423(1):111-121
1. In slices of rat liver, oligomycin inhibited the net transport of Na+ and K+ by a maximum of 30% and endogenous respiration by 25%. These effects were not increased by a number of modifications in the incubation conditions.2. Mitochondria isolated from the slices after incubation showed respiratory control ratios that were somewhat less than in mitochondria from fresh liver, but state 3 respiration retained normal sensitivity to oligomycin.3. Low concentrations of oligomycin or cyanide reduced respiration and ATP levels of the slices but did not affect ion transport unless these levels fell below a definite critical value. In contrast, ouabain and atractyloside each caused substantial degrees of transport inhibition at ATP levels which were in excess of the critical value.4. High concentrations of cyanide and oligomycin reduced ATP contents maximally by 90% and 65%, respectively. Studies of lactate production, and of the effects of arsenite on respiration and ATP levels, suggested that substrate-level phosphorylation in the citric-acid cycle was the major source of the oligomycin-resistant ATP synthesis.5. The results suggest that oligomycin acts in the liver slices primarily as an inhibitor of oxidative phosphorylation, and that this is the cause of the partial inhibition of ion transport. The oligomycin-resistant ion-transporting activity is consistent with the persisting level of ATP synthesis.  相似文献   

6.
1. Chronic ethanol administration to rats for 21–27 days increases the rate of O2 consumption as measured in liver slices. The extra respiration can be abolished by inhibition of the active transport of Na+ and K+. Dinitrophenol activates the respiratory rate in the liver of the treated animals only in the presence of ouabain. 2. Active (ouabain-sensitive) transport of 86Rb and (Na++K+)-stimulated adenosine triphosphatase activity were increased in the livers of the ethanol-treated animals. 3. Chronic ethanol administration also led to a decrease in the phosphorylation potential ([ATP]/[ADP][Pi]) in the liver cell owing to a decrease in [ATP] and an increase in [Pi]. 4. It is suggested that an increased sodium pump activity is responsible for the increased oxidative capacity and for the insensitivity to dinitrophenol observed in the livers of ethanol-treated animals.  相似文献   

7.
Potassium ions at low concentrations stimulate cytokinin-dependent betacyanin synthesis in Amaranthus tricolor seedlings more than other alkali metal ions when tested as the chloride salts. The sequence of relative stimulation is K+ > Rb+ > (Na+ = Li+). Calcium and Mg2+ ions are inhibitory at concentrations > 1 millimolar when tested as chlorides. Anions also have an effect on the degree of alkali metal stimulation in the order PO43− > NO3 > Cl. The high activity of phosphate may be partly due to its chelating effect on inhibitory Ca2+ ions, or to effects on K+ uptake. A mixture of Na+ and K+ in the presence of phosphate is more effective than either cation alone. This result may be due either to effects on tyrosine transport or on the potassium uptake system. Phytochrome-dependent betacyanin synthesis shows the same stimulation by Na+ plus K+. The effect of a number of inhibitors of transport systems on betacyanin accumulation is reported. The possible role of the ionic environment of cells in their metabolic regulation is discussed, particularly in relation to cytokinin action.  相似文献   

8.
Summary Effects of the proton-alkali cation-exchanging ionophore, monensin, on aspects of cellular metabolism and ionic exchanges have been studied in rat tissues in vitro. Incubation of liver slices at 38°C with 0.1 m monensin induced timedependent vesiculation, initially in the Golgi region, reduction of ATP content and of protein synthesis. At 1 m, monensin also reduced net, active movements of K+, Na+, Cl and water in liver slices and inhibited state 3 respiration in isolated mitochondria. The respiratory inhibitor, amytal, similarly reduced ATP content and protein synthesis at concentrations lower than those inhibiting ion transport in slices. Low concentrations of monensin (0.1–1.0 m) had similar effects on ATP and ion transport in slices of adult lung. By contrast, late-fetal liver and lung were much less sensitive to monensin; in these tissues, glycolysis sustained substantial levels of ATP. Monensin also induced vesiculation of the Golgi apparatus in fetal lung cells. It is concluded that by lowering ATP levels, monensin can markedly alter various metabolic activities in those cells which depend primarily on oxidative phosphorylation for their metabolic energy.  相似文献   

9.
The effect of exposure of chick embryo cells to increasing concentrations of Na+ in the culture medium on the subsequent amino acid transport as determined at physiological osmolarity was investigated in detail. It was found that the hyperosmolar treatment stimulated amino acid transport in a dose-dependent manner up to 200 mM Na+. Changes were measurable as early as 1 h after altering Na+ and reached a maximum after 4 h, remaining constant thereafter. The maintenance of this effect required continuous exposure of the cell to high Na+ in the culture medium. Hyperosmolarity-mediated increases in amino acid transport activity by system A have been detected with l-proline and l-alanine. Transport activities of systems ASC and L did not change appreciably after exposure of the cells to high Na+. Inhibition of protein synthesis by cycloheximide or RNA synthesis by actinomycin D (actD) prevented these uptake changes. Kinetic analysis indicated that the stimulation of the activity of transport system A by high Na+ treatment occurred through a mechanism affecting Vmax rather than Km.  相似文献   

10.
86Rb+ uptake by yeast was not only stimulated by Rb+ or K+ but also by Na+. The uptake of 22Na+ was enhanced by both Rb+ and K+, but not by Na+, which was inhibitory at all concentrations applied. Inhibition of 22Na+ uptake by inactive Na+ occurred in two phases: one phase refers to inhibition at low Na+ concentrations and the other to inhibition at high Na+ concentrations. Our results can be qualitatively described by a two-site transport mechanism, having two cation binding sites, which must be occupied with monovalent cations before transport can occur.  相似文献   

11.
The increase in the release of acetylcholine (ACh) from cortical slices of rat brain elicited by the depolarizing agents, ouabain and tityustoxin (TsTX) was compared in the presence of tetrodotoxin, an inhibitor of Na+ transport and of ethyleneglycol tetraacetic acid, a specific chelator of Ca2+. TsTX stimulated the release of ACh independently of K1 but required both Na+ and Ca2+. Unlike ouabain, TsTX failed to inhibit the Na+, K+ -ATPase of rat brain homogenates. The uptake of 24Na+ and of 45Ca2+ by the slices was significantly enhanced by TsTX over the entire incubation period during which this process was compared to TsTX-free controls. A hypothesis of TsTX action is proposed which differs from that necessary to explain the ACh releasing effect of ouabain.  相似文献   

12.
Petr Paucek  Martin Jab?rek 《BBA》2004,1659(1):83-91
The Na+/Ca2+ antiporter was purified from beef heart mitochondria and reconstituted into liposomes containing fluorescent probes selective for Na+ or Ca2+. Na+/Ca2+ exchange was strongly inhibited at alkaline pH, a property that is relevant to rapid Ca2+ oscillations in mitochondria. The effect of pH was mediated entirely via an effect on the Km for Ca2+. When present on the same side as Ca2+, K+ activated exchange by lowering the Km for Ca2+ from 2  to 0.9 μM. The Km for Na+ was 8 mM. In the absence of Ca2+, the exchanger catalyzed high rates of Na+/Li+ and Na+/K+ exchange. Diltiazem and tetraphenylphosphonium cation inhibited both Na+/Ca2+ and Na+/K+ exchange with IC50 values of 10 and 0.6 μM, respectively. The Vmax for Na+/Ca2+ exchange was increased about fourfold by bovine serum albumin, an effect that may reflect unmasking of an autoregulatory domain in the carrier protein.  相似文献   

13.
Summary The effects of prolonged cold exposure of Syrian hamsters on liver membrane (Na+/K+-ATPase activity and on liver intracellular K+ levels was examined. Membrane preparations from cold-acclimated hamsters (6°C for 3 weeks) exhibited significantly higherV max values for (Na+/K+)-ATPase and significantly greater ouabain binding. These data support the view that in the liver of these cold-exposed hamsters, there is an increase in the number of operational pumps. The fact that the intact liver cells (isolated via liver perfusion) from the cold-acclimated hamsters: (a) did not have higher concentrations of intracellular K+ (despite the presence of more operational pumps); and (b) exhibited greater rates of K+ loss when the pumps were inhibited by maximal ouabain suggests that the K+ leak across the liver cell plasma membrane is increased in the cold-acclimated hamsters. Although the physiological significance of these results needs further evaluation, these membrane changes may be of adaptive value for hibernation.Abbreviations CA cold-acclimated - P i inorganic phosphate - KRB Krebs-Ringer-bicarbonate buffer - BSA bovine serum albumin - ECF extracellular fluid - ICF intracellular fluid - dcs dry cell solid - N nitrogen  相似文献   

14.
—(1) Cerebral slices were incubated in Ca2+-free media or in media which contained 2.8 mm -Ca2+. Omission of Ca2+ brought about a drop in creatine phosphate content of 28 per cent, as well as a drop of 3–10 per cent in non-inulin K+ content. There was little change in content of 10-min phosphate or of non-inulin Na+. (2) Ouabain in concentrations of to M increased the loss of K+ from the slice and caused a rise in Na+ content. The changes were most marked in Ca2+-free media. Creatine phosphate levels were depressed by ouabain both in the presence or absence of Ca2+. In the absence of Ca2+, the lowering of phosphocreatine did not occur until significant shifts in K+ had taken place. In contrast, slices incubated in Ca2+-containing media lost creatine phosphate and K+ at about the same rate. (3) When ouabain and labelled phosphate were added simultaneously, there was little difference in the rate of incorporation of label into creatine phosphate in media which differed in Ca2+ concentration. However, incorporation of azP-labelled phosphate into creatine phosphate was decreased by 30–40 per cent in media which lacked Ca2+ when ouabain was added 15 min prior to the labelled phosphate. This change was not observed when the media contained Ca2+. (4) Ouabain did not affect oxidative phosphorylation or respiratory control when added directly to bovine brain mitochondrial preparations. (5) The results suggest that the previously observed depression of respiration brought about by ouabain in Ca2+-deficient media is not a good indicator of the proportion of the cell's metabolism used for active cation transport. Under these conditions, the inhibition of cation transport is accompanied by a drop in slice content of high-energy phosphate which may represent a secondary effect of ouabain, or of cytoplasmic alterations brought about by ouabain, on energy-producing processes.  相似文献   

15.
In previous studies it was found that change in the concentrations of Ca2+, H+, and HPO42− in the incubation medium altered the rates of synthesis of 1,25-dihydroxyvitamin D-3 (1,25(OH)2D-3) by isolated renal mitochondria obtained from D-deficient chicks. The present studies demonstrate that raising the medium concentration of K+ from 1 to 50 mM leads to a 6-fold increase in rate of 1,25(OH)2D-3 synthesis by isolated chick mitochondria; that the magnitude of this K+-dependent stimulation is enhanced by optimal concentrations of calcium (pCa = 5) and phosphate (pPi = 3) (3 mM) but not by pH (from 6.8 to 7.4); that the effect is not produced by similar changes in media Na+ concentration; and that the stimulatory effect of K+ is not blocked by ruthenium red, an inhibitor of calcium transport and of the calcium-dependent stimulation of mitochondrial 1,25(OH)2D-3 synthesis. It was also found taht valinomycin, a K+-specific ionophore, enhanced the sensitivity of the mitochondrial 1α-hydroxylase activity to K+. In the presence of valinomycin, an increase of pK+ to 3 was sufficient to cause a significant stimulation of 1,25(OH)2D-3 synthesis. It was concluded that changes in the ion content of the mitochondrial matrix space regulate the activity of the 1α-hydroxylase.  相似文献   

16.
The Na+-dependent transport of 5-oxoproline into rabbit renal brush-border vesicles was stimulated by a K+ diffusion potential (interior-negative) induced by valinomycin. Na+ salts of two anions of different epithelial permeabilities also affected 5-oxoproline transport. These results show that the Na+-dependent 5-oxoproline transport in renal brush-border vesicles is an electrogenic process which results in a net transfer of positive charge. Maximum transport of 5-oxoproline occurred at an extravesicular pH of 6.0 to 8.0 and over that pH range, 5-oxoproline exists completely as an anion with a negative charge. The simplest stoichiometry consistent with this process is, therefore, the cotransport of one 5-oxoproline anion with two sodium ions. The presence of K+ inside the vesicles stimulated the Na+-dependent transport of 5-oxoproline. This stimulatory effect was specific for K+ and required the presence of Na+. The presence of Na+ gradient was not mandatory for the K+ action. The stimulation by the intravesicular K+ was seen in the presence as well as in the absence of a K+ gradient. Therefore, the increased influx of 5-oxoproline was not coupled to the simultaneous efflux of K+. The presence of K+ in the extravesicular medium alone did not affect the Na+-dependent transport of 5-oxoproline, showing that the site of K+ action was intravesicular. Glutamate did not interact with the Na+-dependent 5-oxoproline transport even in the presence of an outward K+ gradient.  相似文献   

17.
The sodium-dependent entry of proline and glycine into rat renal brushborder membrane vesicles was examined. The high Km system for proline shows no sodium dependence. The low Km system for glycine entry is strictly dependent on a Na+ gradient but shows no evidence of the carrier system having any affinity for Na+. The low Km system for proline and high Km system for glycine transport appear to be shared. Both systems are stimulated by a Na+ gradient and appear to have an affinity for the Na+. The effect of decreasing the Na+ concentration in the ionic gradient is to alter the Km for amino acid entry and, at low Na+ concentrations, to inhibit the V for glycine entry.  相似文献   

18.
Abstract: We have shown previously that in the chick ciliary nerve-iris muscle preparation Na+-dependent high-affinity choline uptake was confined to the nerve terminals. In this paper the sodium-dependent high-affinity choline uptake (SDHACU), which is coupled to acetylcholine (ACh) synthesis, was further characterized by measuring uptake of [3H]choline and its conversion to [3hjach under a variety of ionic and metabolic perturbations. Mannitol equilibration with the extracellular space was found to occur in less than 1 min in this preparation. Na+-dependent choline (Ch+) uptake was shown to be linear for 16 min and to reach an equilibrium before Na+-independent Ch+ uptake, which continued to increase for 60 min. Elevated [K+]0 concentrations inhibited Ch+ uptake and ACh synthesis. Glycolytic and respiratory inhibitors also reduced both processes, as did ouabain and omission of [K+]0. Incubation conditions that reduce transmitter release had no effect on inhibition by high [K+]0. Reduction of SDHACU and sodium-dependent ACh synthesis by depolarization with high [K+]0 or by inhibition of Na, K-ATPase implies that the electrochemical gradients for Ch+ and Na+ are important in providing a driving force for high-affinity Ch+ uptake. The inhibition by metabolic blockers suggests active transport, but the effects may be indirect, caused by reduced Na, K-ATPase activity and alterations in membrane potential. While most metabolic inhibitors exerted parallel effects on both Ch+ uptake and ACh synthesis, in some cases Ch+ uptake was more strongly inhibited than ACh synthesis. This occurred in preparations incubated with high [K+]0 and ouabain. Na+-dependent Ch+ uptake and ACh synthesis were found to be temperature-dependent with a Q10 (20–30°) of 3.6 and 6.6, respectively and a Q10 (30–40°) of 1.3 and 1.0, respectively. Inhibition of acetylcholinesterase by paraoxon increases to 92% the proportion of the Ch+ taken up which is converted to ACh. ACh did not reduce Ch+ transport when present at 100 μM.  相似文献   

19.
Ouabain-sensitive Na+ and K+ fluxes and ATP content were determined in high potassium sheep erythrocytes at different values of membrane potential and internal pH. Membrane potential was adjusted by suspending erythrocytes in media containing different concentrations of MgCl2 and sucrose. Concomitantly either the external pH was changed sufficiently to maintain a constant internal pH or the external pH was kept constant with a resultant change of internal pH. The erythrocytes were preincubated before the flux experiment started in a medium which produced increased ATP content in order to avoid substrate limitation of the pump. p] It was found that an increased cellular pH reduced the rates of active transport of Na+ and K+ without significantly altering the ratio of pumped Na+K+. This reduction was not due to limitation in the supply of ATP although ATP content decreased when internal pH increased. Changes of membrane potential in the range between ?10 and +60 mV at constant internal pH did not affect the rates of active transport of Na+ or K+.  相似文献   

20.
赵宏亮  倪细炉  侯晖  谢沁宓  程昊 《广西植物》2022,42(7):1150-1159
为揭示长苞香蒲(Typha domingensis)对盐生湿地生态系统中Na+和K+的吸收与转运特征,探讨长苞香蒲对盐生湿地的生态修复效果,该研究采用人工模拟盐生湿地的方法,设置CK(对照)、T1(浇灌100 mmol·L-1盐水)、T2(浇灌200 mmol·L-1盐水)及T3(浇灌300 mmol·L-1盐水)4种不同盐浓度的人工湿地生态系统,并分别于5月5日(开始盐胁迫处理,S0)、5月30日(S1)、6月30日(S2)和7月30日(S3)测量其株高和干重、植株地上与地下部分Na+和K+的含量以及底泥和水体中Na+和K+的含量以分析长苞香蒲对盐碱湿地的脱盐作用。结果表明:(1)各处理的长苞香蒲的株高和干重随着处理时间的延长呈增加趋势,但与CK相比,各处理生长量随盐浓度升高出现下降趋势。(2)高浓度盐处理(T3)使长苞香蒲的地上部分和地下部分的Na+分别增加了2.5...  相似文献   

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