共查询到20条相似文献,搜索用时 15 毫秒
1.
The Ca 2+ transport ATPase (SERCA) of sarcoplasmic reticulum (SR) plays an important role in muscle cytosolic signaling, as it stores Ca 2+ in intracellular membrane bound compartments, thereby lowering cytosolic Ca 2+ to induce relaxation. The stored Ca 2+ is in turn released upon membrane excitation to trigger muscle contraction. SERCA is activated by high affinity binding of cytosolic Ca 2+, whereupon ATP is utilized by formation of a phosphoenzyme intermediate, which undergoes protein conformational transitions yielding reduced affinity and vectorial translocation of bound Ca 2+. We review here biochemical and biophysical evidence demonstrating that release of bound Ca 2+ into the lumen of SR requires Ca 2+/H + exchange at the low affinity Ca 2+ sites. Rise of lumenal Ca 2+ above its dissociation constant from low affinity sites, or reduction of the H + concentration by high pH, prevent Ca 2+/H + exchange. Under these conditions Ca 2+ release into the lumen of SR is bypassed, and hydrolytic cleavage of phosphoenzyme may yield uncoupled ATPase cycles. We clarify how such Ca 2+pump slippage does not occur within the time length of muscle twitches, but under special conditions and in special cells may contribute to thermogenesis. 相似文献
2.
A large number of plant Ca 2+/H + exchangers have been identified in endomembranes, but far fewer have been studied for Ca 2+/H + exchange in plasma membrane so far. To investigate the Ca 2+/H + exchange in plasma membrane here, inside-out plasma membrane vesicles were isolated from Arabidopsis thaliana leaves using aqueous two-phase partitioning method. Ca 2+/H + exchange in plasma membrane vesicles was measured by Ca 2+-dependent dissipation of a pre-established pH gradient. The results showed that transport mediated by the Ca 2+/H + exchange was optimal at pH 7.0, and displayed transport specificity for Ca 2+ with saturation kinetics at K m = 47 μM. Sulfate and vanadate inhibited pH gradient across vesicles and decreased the Ca 2+-dependent transport of H + out of vesicles significantly. When the electrical potential across plasma membrane was dissipated with valinomycin and potassium, the rate of Ca 2+/H + exchange increased comparing to control without valinomycin effect, suggesting that the Ca 2+/H + exchange generated a membrane potential (interior negative), i.e. that the stoichiometric ratio for the exchange is greater than 2H +:Ca 2+. Eosin Y, a Ca 2+-ATPase inhibitor, drastically inhibited Ca 2+/H + exchange in plasma membrane as it does for the purified Ca 2+-ATPase in proteoliposomes, indicating that measured Ca 2+/H + exchange activity is mainly due to a plasma membrane Ca 2+ pump. These suggest that calcium (Ca 2+) is transported out of Arabidopsis cells mainly through a Ca 2+-ATPase-mediated Ca 2+/H + exchange system that is driven by the proton-motive force from the plasma membrane H +-ATPase. 相似文献
3.
Calcium transport into tomato ( Lycopersicon esculentum Mill, cv Castlemart) fruit tonoplast vesicles was studied. Calcium uptake was stimulated approximately 10-fold by MgATP. Two ATP-dependent Ca 2+ transport activities could be resolved on the basis of sensitivity to nitrate and affinity for Ca 2+. A low affinity Ca 2+ uptake system ( Km > 200 micromolar) was inhibited by nitrate and ionophores and is thought to represent a tonoplast localized H +/Ca 2+ antiport. A high affinity Ca 2+ uptake system ( Km = 6 micromolar) was not inhibited by nitrate, had reduced sensitivity to ionophores, and appeared to be associated with a population of low density endoplasmic reticulum vesicles that contaminated the tonoplast-enriched membrane fraction. Arrhenius plots of the temperature dependence of Ca 2+ transport in tomato membrane vesicles showed a sharp increase in activation energy at temperatures below 10 to 12°C that was not observed in red beet membrane vesicles. This low temperature effect on tonoplast Ca 2+/H + antiport activity could only by partially ascribed to an effect of low temperature on H +-ATPase activity, ATP-dependent H + transport, passive H + fluxes, or passive Ca 2+ fluxes. These results suggest that low temperature directly affects Ca 2+/H + exchange across the tomato fruit tonoplast, resulting in an apparent change in activation energy for the transport reaction. This could result from a direct effect of temperature on the Ca 2+/H + exchange protein or by an indirect effect of temperature on lipid interactions with the Ca 2+/H + exchange protein. 相似文献
4.
Summary We have examined the effect of second messengers on ATP-driven H + transport in an H + ATPase-bearing endosomal fraction isolated from rabbit renal cortex. cAMP (0.1 mm) had no effect on H + transport. Acridine orange fluorescence in the presence of 0.5 mm Ca 2+ (+1 mm EGTA) was 19±6% of control. Inhibition of ATP-driven H + transport by Ca 2+ was concentration dependent; 0.25 and 0.5 mm Ca 2+ (+1 mm EGTA) inhibited acridine orange fluorescence by 50 and 80%, respectively. Ca 2+ also produced a concentration-dependent increase in the rate of pH-gradient dissipation. Ca 2+ did not affect ATP hydrolysis. ATP-dependent Br – uptake was virtually unchanged in the presence of 0.5 mm Ca 2+ (+1 mm EGTA). These vesicles were also shown to transport Ca 2+ in an ATP-dependent mode. Inositol 1, 4, 5-trisphosphate had no effect on ATP-dependent Ca 2+ uptake. These results are consistent with the co-existence of an H + ATPase and an H +/Ca 2+ exchanger on these endosomes, the latter transport system using the H + gradient to energize Ca 2+ uptake. Attempts to demonstrate an H +/Ca 2+ antiporter in the absence of ATP have been unsuccessful. Yet, when a pH gradient was established by preincubation with ATP and residual ATP was subsequently removed by hexokinase + glucose, stimulation of Ca 2+ uptake could be demonstrated. A Ca 2+-dependent increase in H + permeability and an ATP-dependent Ca 2+ uptake might have important implications for the regulation of vacuolar H + ATPase activity as well as the homeostasis of cytosolic Ca 2+ concentration. 相似文献
5.
Summary In rabbit ileum, Ca 2+/calmodulin (CaM) appears to be involved in physiologically inhibiting the linked NaCl absorptive process, since inhibitors of Ca 2+/CaM stimulate linked Na + and Cl – absorption. The role of Ca 2+/CaM-dependent phosphorylation in regulation of the brush-border Na +/H + antiporter, which is believed to be part of the neutral linked NaCl absorptive process, was studied using purified brush-border membrane vesicles, which contain both the Na +/H + antiporter and Ca 2+/CaM-dependent protein kinase(s) and its phosphoprotein substrates. Rabbit ileal villus cell brush-border membrane vesicles were prepared by Mg precipitation and depleted of ATP. Using a freezethaw technique, the ATP-depleted vesicles were loaded with Ca 2+, CaM, ATP and an ATP-regenerating system consisting of creatine kinase and creatine phosphate. The combination of Ca 2+/CaM and ATP inhibited Na +/H + exchange by 45±13%. This effect was specific since Ca 2+/CaM and ATP did not alter diffusive Na + uptake, Na +-dependent glucose entry, or Na + or glucose equilibrium volumes. The inhibition of the Na +/H + exchanger by Ca 2+/CaM/ATP was due to an effect on the V
max and not on the K
m
for Na +. In the presence of CaM and ATP, Ca 2+ caused a concentration-dependent inhibition of Na + uptake, with an effect 50% of maximum occurring at 120 nm. This Ca 2+ concentration dependence was similar to the Ca 2+ concentration dependence of Ca 2+/CaM-dependent phosphorylation of specific proteins in the vesicles. The Ca 2+/CaM/ATP-inhibition of Na +/H + exchange was reversed by W 13, a Ca 2+/CaM antagonist, but not by a hydrophobic control, W 12, or by H-7, a protein kinase C antagonist. we conclude that Ca 2+, acting through CaM, regulates ileal brush-border Na +/H + exchange, and that this may be involved in the regulation of neutral linked NaCl absorption. 相似文献
6.
Phosphoenolpyruvate was found to depress extra oxygen consumption associated with Ca 2+-induced respiratory jump by rat heart mitochondria. Addition of phosphoenolpyruvate to mitochondria which have accumulated Ca 2+ in the presence of glutamate and inorganic phosphate causes the release of Ca 2+ from mitochondria. The phosphoenolpyruvate-stimulated Ca 2+ efflux can be observed with mitochondria loaded with low initial Ca 2+ concentration (0.12 mM) in the incubation medium. Measurements of mitochondrial H + translocation produced by addition of Ca 2+ to respiring mitochondria show that phosphoenolpyruvate depresses H + ejection and enhances H + uptake by mitochondria. The Ca 2+-releasing effect of phosphoenolpyruvate was found to be significantly stronger than that produced by rotenone when added to mitochondria loaded with Ca 2+ in the presence of glutamate and inorganic phosphate. Dithiothreitol cannot overcome the effect of phosphoenolpyruvate on mitochondrial Ca 2+ transport. 相似文献
7.
A rapid loss of accumulated Ca 2+ is produced by addition of H + to isolated heart mitochondria. The H +-dependent Ca + efflux requires that either (a) the NAD(P)H pool of the mitochondrion be oxidized, or (b) the endogenous adenine nucleotides be depleted. The loss of Ca 2+ is accompanied by swelling and loss of endogenous Mg 2–. The rate of H +-dependent Ca 2+ efflux depends on the amount of Ca 2+ and P i taken up and the extent of the pH drop imposed. In the absence of ruthenium red the H +-induced Ca 2+-efflux is partially offset by a spontaneous re-accumulation of released Ca 2+. The H +-induced Ca 2+ efflux is inhibited when the P i transporter is blocked with N-ethylmaleimide, is strongly opposed by oligomycin and exogenous adenine nucleotides (particularly ADP), and inhibited by nupercaine. The H +-dependent Ca 2+ efflux is decreased markedly when Na + replaces the K + of the suspending medium or when the exogenous K +/H + exchanger nigericin is present. These results suggest that the H +-dependent loss of accumulated Ca 2+ results from relatively nonspecific changes in membrane permeability and is not a reflection of a Ca 2+/H + exchange reaction. 相似文献
8.
Phosphorylation/dephosphorylation of the plasma-membrane H +-ATPase (EC 3.6.1.35) could act as a regulatory mechanism to control its activity. In this work, a plasmalemma-enriched fraction
from maize roots and a partially purified H +-ATPase were used to investigate the effects of Ca 2+ and calmodulin on the H +-ATPase activity and on its phosphorylation status. Both the hydrolytic and the proton-pumping activities were reduced approximately
50% by micromolar Ca 2+ concentrations while calmodulin did not show any effect either alone or in the presence of Ca 2+. The lack of effect of calmodulin antagonists indicated that calmodulin was not involved in this response. The addition of
staurosporine, a kinase inhibitor, abolished the inhibitory effect of Ca 2+. Phosphorylation of plasma membrane and partially purified H +-ATPase showed the same behavior. In the presence of Ca 2+ a polypeptide of 100 kDa was phosphorylated. This polypeptide cross-reacted with antibodies raised against the H +-ATPase of maize roots. The autoradiogram of the immunodetected protein clearly showed that this polypeptide, which corresponds
to the H +-ATPase, was phosphorylated. Additional clear evidence comes from the immunoprecipitation experiments: the data obtained show
that the H +-ATPase activity is indeed influenced by its state of phosphorylation.
Received: 19 October 1998 / Accepted: 23 February 1999 相似文献
9.
Abstract: The features of Ca 2+ fluxes, the importance of the Ca 2+ pump‐mediated H +/Ca 2+ exchanges at plasmalemma level, and the possible involvement of Ca 2+‐ATPase activity in ABA‐induced changes of H + fluxes were studied in Egeria densa leaves. The results presented show that, while in basal conditions no net Ca 2+ flux was evident, a conspicuous Ca 2+ influx (about 1.1 ìmol g ?1 FW h ?1) occurred. The concomitant efflux of Ca 2+ was markedly reduced by treatment with 5 íM eosin Y (EY), a specific inhibitor of the Ca 2+‐ATPase, that completely blocked the transport of Ca 2+ after the first 20 ‐ 30 min. The decrease in Ca 2+ efflux induced by EY was associated with a significant increase in net H + extrusion (?ÄH +) and a small but significant cytoplasmic alkalinization. The shift of external [Ca 2+] from 0.3 to 0.2 mM (reducing Ca 2+ uptake by about 30 %) and the hindrance of Ca 2+ influx by La 3+ were accompanied by progressively higher ?ÄH + increases, in agreement with a gradual decrease in the activity of a mechanism counteracting the Ca 2+ influx by an nH +/Ca 2+ exchange. The ABA‐induced decreases in ?ÄH + and pH cyt were accompanied by a significant increase in Ca 2+ efflux, all these effects being almost completely suppressed by EY, in line with the view that the ABA effects on H + fluxes are due to activation of the plasmalemma Ca 2+‐ATPase. These results substantially stress the high sensitivity and efficacy of the plasmalemma Ca 2+ pump in removing from the cytoplasm the Ca 2+ taken up, and the importance of the contribution of Ca 2+ pump‐mediated H +/Ca 2+ fluxes in bringing about global changes of H + fluxes at plasmalemma level. 相似文献
10.
Washing corn ( Zea mays L.) root tissue in water causes loss of about one-third of the exchangeable Ca 2+ over the first 10 to 15 minutes. Upon transfer to K +-containing solutions, the tissue shows a short period of rapid K + influx which subsequently declines. Addition of 0.1 millimolar Ca 2+ decreases the initial rapid K + influx, but increases the sustained rate of K + and Cl − uptake. It was confirmed (Elzam and Hodges 1967 Plant Physiol 42: 1483-1488) that 0.1 millimolar Ca 2+ is more effective than higher concentrations for the initial inhibition, and that Mg 2+ will substitute. The inhibition arises from a mild shock affect of restoring Ca2+. With 0.1 millimolar Ca2+ net H+ efflux is blocked for 10 to 15 minutes and the cells are depolarized by about 30 millivolts. However, 1 millimolar Ca2+ rapidly produces increased K+ influx and blocks net H+ efflux for only a few minutes; blockage is preceded by a brief net H+ influx which may restore and increase ion transport by reactivating the plasmalemma H+-ATPase. Stimulation of electrogenic H+-pumping with fusicoccin eliminates the shock responses and minimizes Ca2+ effects on K+ influx. Fusicoccin also strongly decreases Ca2+ influx, but has no effect on Ca2+ efflux. Ice temperatures and high pH decreased Ca2+ efflux, but uncoupler and chlorpromazine did not. It is suggested that the inhibitory and promotive actions of Ca2+ are manifested through decreases or increases in the protonmotive force. 相似文献
11.
The primary or secondary energized transport of Ca 2+, Mg 2+ and H + into tonoplast membrane vesicles from roots of Zea mays L. seedlings was studied photometrically by using the fluorescent Ca 2+ indicator Indo 1 and the pH indicator neutral red. The localization of an ATP-dependent, vanadate-sensitive Ca 2+ pump on tonoplast-type vesicles was demonstrated by the co-migration of the Ca 2+-pumping and tonoplast H +-pyrophosphatase (PP iase) activity on continuous sucrose density gradients. In ER-membrane fractions, only a low Ca 2+-pumping activity could be detected. The ATP-dependent Ca 2+ uptake into tonoplast vesicles (using Ca 2+ concentrations from 0.8–1 μM) was completely inhibited by the Ca 2+ ionophore ionomycin (1 μM) whereas the protonophore nigericin (1 μM) which eliminates ATP-dependent intravesicular H + accumulation had no effect. Vanadate (IC 50 = 43 μM) and diethylstilbesterol (IC 50 = 5.2 μM) were potent inhibitors of this type of Ca 2+ transport. The nucleotides GTP, UTP, ITP, and ADP gave 27%–50% of the ATP-dependent activity ( K m = 0.41 mM). From these results, it was suggested that this ATP-dependent high-affinity Ca 2+ transport mechanism is the only functioning Ca 2+ transporter of the tonoplast under in-vivo conditions i.e. under the low cytosolic Ca 2+ concentration. In contrast, the secondary energized Ca 2+-transport mechanism of the tonoplast, the low-affinity Ca 2+/H +-antiporter, which was reported to allow the uptake of Ca 2+ in exchange for H +, functions chiefly as an Mg 2+ transporter under physiological conditions because cytosolic Mg 2+ is several orders of magnitude higher than the Ca 2+ concentration. This conclusion was deduced from experiments showing that Mg 2+ ions in a concentration range of 0.01 to 1 mM triggered a fast efflux of H + from acid-loaded vesicles. Furthermore, the proton-pumping activity of the tonoplast H +-ATPase and H +-PP iase was found to be influenced by Ca 2+ differently from and independently of the Mg 2+ concentration. Calcium was a strong inhibitor for the H +-PP iase (IC 50 = 18 μM, Hill coefficient nH = 1.7) but a weak one for the H +-ATPase (IC 50 = 330 μM, nH = 1). From these results it is suggested that at the tonoplast membrane a functional interaction exists between (i) the Ca 2+-and Mg 2+-regulated H +-PP iase, (ii) the newly described high-affinity Ca 2+-AT-Pase, (iii) the low-affinity Mg 2+(Ca 2+)/H +-antiporter and (iv) the H 2+-ATPase. 相似文献
12.
An endogenous soluble protease has been demonstrated to unmask a Ca 2+-stimulated ATPase activity in purified dog gastric microsomes. The presence of ATP during protease treatment appears essential for the manifestation of the gastric Ca 2+-stimulated ATPase activity. The endogenous protease appears to have trypsin-like activity, since soybean trypsin inhibitor completely blocks the protease effect. Manifestation of the Ca 2+-stimulated ATPase occurs without affecting the microsomal (H + +K +)-ATPase activity and associated H + uptake ability. The unmasked Ca 2+-stimulated ATPase appears insensitive to calmodulin. Possible roles of the enzyme in the regulation of gastric H + transport have been discussed. 相似文献
13.
Net fluxes of Ca 2+, H + and K + were measured from intact Chara australis cells and from isolated cell walls, using ion-selective microelectrodes. In both systems, a stimulation in Ca 2+ efflux (up to 100 nmol m ?2 s ?1, from an influx of ~40 nmol m ?2 s ?1) was detected as the H + or K + concentration was progressively increased in the bathing solution (pH 7.0 to 4.6 or K + 0.2 to 10mol m ?3, respectively). A Ca 2+ influx of similar size occurred following the reverse changes. These fluxes decayed exponentially with a time constant of about 10 min. The threshold pH for Ca 2+ efflux (pH 5.2) is similar to a reported pH threshold for acid-induced wall extensibility in a closely related characean species. Application of NH 4+ to intact cells caused prolonged H + efflux and also transient Ca 2+ efflux. We attribute all these net Ca 2+ fluxes to exchange in the wall with H + or K +. A theoretical treatment of the cell wall ion exchanges, using the ‘weak acid Donnan Manning’ (WADM) model, is given and it agrees well with the data. The role of Ca 2+ in the cell wall and the effect of Ca 2+ exchanges on the measured fluxes of other ions, including bathing medium acidification by H + efflux, are discussed. 相似文献
14.
Bongkrekic acid and atractyloside, inhibitors of adenine nucleotide translocase, do not inhibit Ca 2+ uptake and H + production by pig heart mitochondria. However, bongkrekic acid, but not atractyloside, inhibits dinitrophenol-induced Ca 2+ efflux and H + uptake. Conversely, ruthenium red blocks Ca 2+ uptake and H + production but does not prevent dinitrophenol-induced Ca 2+ efflux and H + uptake by mitochondria. These results suggest that mitochondrial Ca 2+ uptake and release exist as two independent pathways. The efflux of Ca 2+ from mitochondria is mediated by a bongkrekic acid sensitive component which is apparently not identical to the ruthenium red sensitive Ca 2+ uptake carrier. 相似文献
15.
During the ascidian sperm reaction the single large cylindrical mitochondrion which lies next to the nucleus in the head swells, becomes spherical, and migrates along the tail to be lost when it reaches the end. This sequence is initiated by eggs, egg water, high pH, low Na +, or the ionophore X537A. Accompanying the sperm reaction induced by low Na + are H + efflux and Ca 2+ influx in a ratio of near 100:1 as determined by 45Ca 2+ and atomic absorption analysis. Simultaneous pH and Ca 2+ electrode measurements suggest that the movement of H + begins 10–13 sec before the movement of Ca 2+. Ca 2+ uptake can be inhibited by verapamil without affecting H + efflux or the sperm reaction. Acid release and Ca 2+ uptake are proportional to the initial pH of the medium when the reaction is triggered by high pH. Acid release initiated by low Na + is proportional to Ca 2+ concentrations above 2 m M. H + and Ca 2+ movements differ in magnitude, kinetics, and inhibition by verapamil, thus suggesting that H + is probably not exchanged for Ca 2+. Instead we propose that loss of H + triggers the uptake of Ca 2+, which initiates the sperm reaction. 相似文献
16.
Summary Recently Plieth et al. [Protoplasma (1997) 198: 107–124; 199: 223] gave a quantitative picture of the Ca 2+ and H + buffers in green algae which we would like to comment. In that paper a mechanistic model was derived which describes the relationship between cytosolic Ca 2+ and H + assuming that Ca 2+ and H + interact with the same binding site of a Ca 2+-H +-exchange buffer. But the increase of the cytosolic free Ca 2+ concentration observed upon acidification can alternatively be described by a co-operative ( n=2) protonation of a Ca 2+/H +-binding buffer pointing to an allosteric mechanism of Ca 2+ liberation. Furthermore we present evidences that the cytosolic buffer capacities for H + (90 mM/pH) and Ca 2+ (20 mM/pCa) given for Eremosphaera viridis were overestimated by a factor of three and three orders of magnitude, respectively.Abbreviations [Ca 2+] c
free cytosolic
- Ca 2+
concentration 相似文献
17.
A transient Ca 2+ release from preloaded mitochondria can be induced by a sudden decrease in the pH of the outer medium from 8.0 or 7.4 to 6.8. In the presence of inorganic phosphate the released Ca 2+ is not taken up again. Upon Ca 2+ addition to respiring mitochondria the mitochondrial membrane potential (Δ♀) decreases to a new resting level. A further decrease in Δ♀ occurs after the decrease in pH from 7.4 to 6.8, concomitant with the reuptake phase of the Ca 2+ release. Phosphate, EGTA, and ruthenium red restore Δ♀ to its initial level. If phosphate is present initially, only transient changes in Δ♀ occur upon addition of Ca 2+ or H + ions. Only a small transient change in Δ♀ upon H + ion addition is seen in the absence of accumulated Ca 2+. La 3+, a competitive inhibitor of Ca 2+ transport, prevents the H + ion-induced Ca 2+ efflux, whereas this is not the case in the presence of the noncompetitive inhibitor ruthenium red. Ruthenium red, however, prevents the reuptake phase. Mg 2+, an inhibitor of the surface binding of Ca 2+, has no or only a slight effect on the H + ion-induced Ca 2+ release. Mitochondria preloaded with Ca 2+ release a small fraction of Ca 2+ during the subsequent uptake of another pulse of Ca 2+. The results indicate that at least one pool of mitochondrial Ca 2+ exists in a mobile state. The possible existence of a exchanger in the mitochondrial membrane is discussed. 相似文献
18.
Ca 2+ transport by the sarcoplasmic/endoplasmic reticulum Ca 2+ ATPase (SERCA) is sensitive to monovalent cations. Possible K + binding sites have been identified in both the cytoplasmic P-domain and the transmembrane transport-domain of the protein. We measured Ca 2+ transport into SR vesicles and SERCA ATPase activity in the presence of different monovalent cations. We found that the effects of monovalent cations on Ca 2+ transport correlated in most cases with their direct effects on SERCA. Choline +, however, inhibited uptake to a greater extent than could be accounted for by its direct effect on SERCA suggesting a possible effect of choline on compensatory charge movement during Ca 2+ transport. Of the monovalent cations tested, only Cs + significantly affected the Hill coefficient of Ca 2+ transport ( nH). An increase in nH from ∼2 in K + to ∼3 in Cs + was seen in all of the forms of SERCA examined. The effects of Cs + on the maximum velocity of Ca 2+ uptake were also different for different forms of SERCA but these differences could not be attributed to differences in the putative K + binding sites of the different forms of the protein. 相似文献
19.
Electrical signals, including action potential (AP), play an important role in plant adaptation to the changing environmental conditions. Experimental and theoretical investigations of the mechanisms of AP generation are required to understand the relationships between environmental factors and electrical activity of plants. In this work we have elaborated a mathematical model of AP generation, which takes into account the participation of vacuole in the generation of electrical response. The model describes the transporters of the plasma membrane (Ca 2+, Cl –, and K + channels, H +- and Ca 2+-ATPases, H +/K + antiporter, and 2H +/Cl – symporter) and the tonoplast (Ca 2+, Cl –, and K + channels; H +- and Ca 2+-ATPases; H +/K +, 2H +/Cl –, and 3H +/Ca 2+ antiporters), with due consideration of their regulation by second messengers (Ca 2+ and IP3). The apoplastic, cytoplasmic and vacuolar buffers are also described. The properties of the simulated AP are in good agreement with experimental data. The AP model describes the attenuation of electrical signal with an increase in the vacuole area and volume; this effect is related to a decrease in the Ca 2+ spike magnitude. The electrical signal was weakly influenced by the K + and Cl – content in the vacuole. It was also shown that the contribution of vacuolar IP 3-dependent Ca 2+ channels into the generation of calcium spike during AP was insignificant with the given parameters of the model. The results provide theoretical evidence for the significance of the vacuolar area and volume in plant cell excitability. 相似文献
20.
A pH-sensitive electrode was applied to measure activity of H + ions in the medium surrounding excitable cells of pumpkin ( Cucurbita pepo L.) seedlings during cooling-induced generation of action potential (AP). Reversible alkalization shifts were found to occur synchronously with AP, which could be due to the influx of H + ions from external medium into excitable cells. Ethacrynic acid (an anion channel blocker) reduced the AP amplitude but had no effect on the transient alkalization of the medium. An inhibitor of plasma membrane H +-ATPase, N,N’-dicyclohexylcarbodiimide suppressed both the AP amplitude and the extent of alkalization. In experiments with plasma membrane vesicles, the hydrolytic H +-ATPase activity was subjected to inhibition by Ca 2+ concentrations in the range characteristic of cytosolic changes during AP generation. The addition of a calcium channel blocker verapamil and a chelating agent EGTA to inhibit Ca 2+ influx from the medium eliminated the AP spike and diminished reversible alkalization of the external solution. An inhibitor of protein kinase, H-7 alleviated the inhibitory effect of Ca 2+ on hydrolytic H +-ATPase activity in plasma membrane vesicles and suppressed the reversible alkalization of the medium during AP generation. The results provide evidence that the depolarization phase of AP is associated not only with activation of chloride channels and Cl ? efflux but also with temporary suppression of plasma membrane H +-ATPase manifested as H + influx. The Ca 2+-induced inhibition of the plasma membrane H +-ATPase is supposedly mediated by protein kinases. 相似文献
|