共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary The (Ca2+ + Mg2+) ATPase which serves as a Ca2+ pump in the kidney basolateral membranes is essential to the maintenance of an intracellular Ca2+ concentration optimal for kidney function. Since atrial natriuretic peptide (ANP) is known to participate in the Ca2+ homeostasis mechanism, altered levels of ANP in diabetes may vary the pump activity and consequently the kidney function. In order to examine the modulatory role of ANP on (Ca2+ + Mg2+) ATPase in short- (6 weeks) and long-term (6 months) diabetes, rats were injected with streptozotocin (65 mg/kg body wt, i.v.). At 6 weeks, the plasma ANP was decreased whereas, ANP-receptor binding in the kidney basolateral membrane was increased. In contrast, there was an increased plasma ANP and decreased ANP receptor binding at 6 months. Insulin treatment to diabetic animals normalized these parameters. The (Ca2+ + Mg2+) ATPase activity was unchanged both at 6 weeks and 6 months. Our results demonstrate that the unchanged Ca2+ pump activity in short-term and long-term diabetes serves to maintain the Ca2+ homeostasis in the kidney cells and thus may maintain the hyperfiltration state in diabetes. Unaltered (Ca2+ + Mg2+) ATPase is achieved by the initial up-regulation and subsequent down-regulation of the ANP receptors. 相似文献
2.
The present study aimed to clarify the existence of a Na+/Ca2+ antiport device in kidney tubular epithelial cells discussed in the literature to represent the predominant mechanistic device for Ca2+ reabsorption in the kidney. (1) Inside-out oriented plasma membrane vesicles from tubular epithelial cells of guinea-pig kidney showed an ATP-driven Ca2+ transport machinery similar to that known to reside in the plasma membrane of numerous cell types. It was not affected by digitalis compounds which otherwise are well-documented inhibitors of Ca2+ reabsorption. (2) The vesicle preparation contained high, digitalis-sensitive (Na++K+-ATPase activities indicating its origin from the basolateral portion of plasma membrane. (3) The operation of Na+/Ca2+ antiport device was excluded by the findings that steep Ca2+ gradients formed by ATP-dependent Ca2+ accumulation in the vesicles were not discharged by extravesicular Na+, and did not drive 45Ca2+ uptake into the vesicles via a Ca2+-45Ca2+ exchange. (4) The ATP-dependent Ca2+ uptake into the vesicles became increasingly depressed with time by extravesicular Na+. This was not due to an impairment of the Ca2+ pump itself, but caused by Na+/Ca2+ competition for binding sites on the intravesicular membrane surface shown to be important for high Ca2+ accumulation in the vesicles. (5) Earlier observations on Na+-induced release of Ca2+ from vesicles pre-equilibrated with Ca2+, seemingly favoring the existence of a Na+/Ca2+ antiporter in the basolateral plasma membrane, were likewise explained by the occurrence of Na+/Ca2+ competition for binding sites. The weight of our findings disfavors the transcellular pathway of Ca2+ reabsorption through tubule epithelium essentially depending on the operation of a Na+/Ca2+ antiport device. 相似文献
3.
Kinetic properties of the ATP-dependent Ca2+ pump and the Na+/Ca2+ exchange system in basolateral membranes from rat kidney cortex 总被引:1,自引:0,他引:1
M. P. E. van Heeswijk J. A. M. Geertsen C. H. van Os 《The Journal of membrane biology》1984,79(1):19-31
Summary Basolateral plasma membranes from rat kidney cortex have been purified 40-fold by a combination of differential centrifugation, centrifugation in a discontinuous sucrose gradient followed by centrifugation in 8% percoll. The ratio of leaky membrane vesicles (L) versus right-side-out (RO) and inside-out (IO) resealed vesicles appeared to be LROIO=431. High-affinity Ca2+-ATPase, ATP-dependent Ca2+ transport and Na+/Ca2+ exchange have been studied with special emphasis on the relative transport capacities of the two Ca2+ transport systems. The kinetic parameters of Ca2+-ATPase activity in digitonin-treated membranes are:K
m
=0.11 m Ca2+ andV
max=81±4 nmol Pi/min·mg protein at 37°C. ATP-dependent Ca2+ transport amounts to 4.3±0.2 and 7.4±0.3 nmol Ca2+/min·mg protein at 25 and 37°C, respectively, with an affinity for Ca2+ of 0.13 and 0.07 m at 25 and 37°C. After correction for the percentage of IO-resealed vesicles involved in ATP-dependent Ca2+ transport, a stoichiometry of 0.7 mol Ca2+ transported per mol ATP is found for the Ca2+-ATPase. In the presence of 75mm Na+ in the incubation medium ATP-dependent Ca2+ uptake is inhibited 22%. When Na+ is present at 5mm an extra Ca2+ accumulation is observed which amounts to 15% of the ATP-dependent Ca2+ transport rate. This extra Ca2+ accumulation induced by low Na+ is fully inhibited by preincubation of the vesicles with 1mm ouabain, which indicates that (Na+–K+)-ATPase generates a Na+ gradient favorable for Ca2+ accumulation via the Na+/Ca2+ exchanger. In the absence of ATP, a Na+ gradient-dependent Ca2+ uptake is measured which rate amounts to 5% of the ATP-dependent Ca2+ transport capacity. The Na+ gradient-dependent Ca2+ uptake is abolished by the ionophore monensin but not influenced by the presence of valinomycin. The affinity of the Na+/Ca2+ exchange system for Ca2+ is between 0.1 and 0.2 m Ca2+, in the presence as well as in the absence of ATP. This affinity is surprisingly close to the affinity measured for the ATP-dependent Ca2+ pump. Based on these observations it is concluded that in isolated basolateral membranes from rat kidney cortex the Ca2+-ATPase system exceeds the capacity of the Na+/Ca2+ exchanger four- to fivefold and it is therefore unlikely that the latter system plays a primary role in the Ca2+ homeostasis of rat kidney cortex cells. 相似文献
4.
Kannan Subburaj Elimban Vijayan Fandrich Robert R. Kardami Elissavet Dhalla Naranjan S. 《Molecular and cellular biochemistry》1999,197(1-2):187-194
Cardiac plasma membrane Ca2+/Mg2+ ecto-ATPase (myoglein) requires millimolar concentrations of either Ca2+ or Mg2+ for maximal activity. In this paper, we report its localization by employing an antiserum raised against the purified rat cardiac Ca2+/Mg2+ ATPase. As assessed by Western blot analysis, the antiserum and the purified immunoglobulin were specific for Ca2+/Mg2+ ecto-ATPase; no cross reaction was observed towards other membrane bound enzymes such as cardiac sarcoplasmic reticulum Ca2+-pump ATPase or sarcolemmal Ca2+-pump ATPase. On the other hand, the cardiac Ca2+/Mg2+ ecto-ATPase was not recognized by antibodies specific for either cardiac sarcoplasmic reticulum Ca2+-pump ATPase or plasma membrane Ca2+-pump ATPase. Furthermore, the immune serum inhibited the Ca2+/Mg2+ ecto-ATPase activity of the purified enzyme preparation. Immunofluorescence of cardiac tissue sections and neonatal cultured cardiomyocytes with the Ca2+/Mg2+ ecto-ATPase antibodies indicated the localization of Ca2+/Mg2+ ecto-ATPase in association with the plasma membrane of myocytes, in areas of cell-matrix or cell-cell contact. Staining for the Ca2+/Mg2+ ecto-ATPase was not cardiac specific since the antibodies detected the presence of membrane proteins in sections from skeletal muscle, brain, liver and kidney. The results indicate that Ca2+/Mg2+ ecto-ATPase is localized to the plasma membranes of cardiomyocytes as well as other tissues such as brain, liver, kidney and skeletal muscle. 相似文献
5.
Ca2+ pump and Ca2+/H+ antiporter in plasma membrane vesicles isolated by aqueous two-phase partitioning from corn leaves 总被引:3,自引:0,他引:3
Summary Plasma membrane vesicles, which are mostly right side-out, were isolated from corn leaves by aqueous two-phase partitioning method. Characteristics of Ca2+ transport were investigated after preparing inside-out vesicles by Triton X-100 treatment.45Ca2+ transport was assayed by membrane filtration technique. Results showed that Ca2+ transport into the plasma membrane vesicles was Mg-ATP dependent. The active Ca2+ transport system had a high affinity for Ca2+(K
m
(Ca2+)=0.4 m) and ATP(K
m
(ATP)=3.9 m), and showed pH optimum at 7.5. ATP-dependent Ca2+ uptake in the plasma membrane vesicles was stimulated in the presence of Cl– or NO
3
–
. Quenching of quinacrine fluorescence showed that these anions also induced H+ transport into the vesicles. The Ca2+ uptake stimulated by Cl– was dependent on the activity of H+ transport into the vesicles. However, carbonylcyanidem-chlorophenylhydrazone (CCCP) and VO
4
3–
which is known to inhibit the H+ pump associated with the plasma membrane, canceled almost all of the Cl–-stimulated Ca2+ uptake. Furthermore, artificially imposed pH gradient (acid inside) caused Ca2+ uptake into the vesicles. These results suggest that the Cl–-stimulated Ca2+ uptake is caused by the efflux of H+ from the vesicles by the operation of Ca2+/H+ antiport system in the plasma membrane. In Cl–-free medium, H+ transport into the vesicles scarcely occurred and the addition of CCCP caused only a slight inhibition of the active Ca2+ uptake into the vesicles. These results suggest that two Ca2+ transport systems are operating in the plasma membrane from corn leaves, i.e., one is an ATP-dependent active Ca2+ transport system (Ca2+ pump) and the other is a Ca2+/H+ antiport system. Little difference in characteristics of Ca2+ transport was observed between the plasma membranes isolated from etiolated and green corn leaves. 相似文献
6.
In resting muscle, cytoplasmic Ca2+ concentration is maintained at a low level by active Ca2+ transport mediated by the Ca2+ ATPase from sarcoplasmic reticulum. The region of the protein that contains the catalytic site faces the cytoplasmic side of the membrane, while the transmembrane helices form a channel-like structure that allows Ca2+ translocation across the membrane. When the coupling between the catalytic and transport domains is lost, the ATPase mediates Ca2+ efflux as a Ca2+ channel. The Ca2+ efflux through the ATPase channel is activated by different hydrophobic drugs and is arrested by ligands and substrates of the ATPase at physiological pH. At acid pH, the inhibitory effect of cations is no longer observed. It is concluded that the Ca2+ efflux through the ATPase may be sufficiently fast to support physiological Ca2+ oscillations in skeletal muscle, that occur mainly in conditions of intracellular acidosis. 相似文献
7.
Studies of Ca2+ transport pathways in exocrine gland cells have been useful, chiefly because of the polarized nature of the secretory epithelial cells. In pancreatic acinar cells, for example, Ca2+ reloading of empty intracellular stores can occur solely via Ca2+ entry through the basal part of the plasma membrane. On the other hand, the principal site for intracellular Ca2+ release—with the highest concentration of inositol 1,4,5-trisphosphate (IP3) receptors—is in the apical secretory pole close to the apical plasma membrane. This apical part of the plasma membrane contains the highest density of Ca2+ pumps and is therefore the principal site for Ca2+ extrusion. On the basis of the known properties of Ca2+ entry and exit pathways in exocrine gland cells, the mechanisms controlling Ca2+ exit and entry are discussed in relation to recent direct information about Ca2+ transport into and out of the endoplasmic reticulum (ER) and the mitochondria in these cells. 相似文献
8.
Giuseppe Inesi Francesco Tadini-Buoninsegni 《Journal of cell communication and signaling》2014,8(1):5-11
The Ca2+ transport ATPase (SERCA) of sarcoplasmic reticulum (SR) plays an important role in muscle cytosolic signaling, as it stores Ca2+ in intracellular membrane bound compartments, thereby lowering cytosolic Ca2+ to induce relaxation. The stored Ca2+ is in turn released upon membrane excitation to trigger muscle contraction. SERCA is activated by high affinity binding of cytosolic Ca2+, whereupon ATP is utilized by formation of a phosphoenzyme intermediate, which undergoes protein conformational transitions yielding reduced affinity and vectorial translocation of bound Ca2+. We review here biochemical and biophysical evidence demonstrating that release of bound Ca2+ into the lumen of SR requires Ca2+/H+ exchange at the low affinity Ca2+ sites. Rise of lumenal Ca2+ above its dissociation constant from low affinity sites, or reduction of the H+ concentration by high pH, prevent Ca2+/H+ exchange. Under these conditions Ca2+ release into the lumen of SR is bypassed, and hydrolytic cleavage of phosphoenzyme may yield uncoupled ATPase cycles. We clarify how such Ca2+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
9.
The Mg2+-dependency of Ca2+-induced ATP hydrolysis is studied in basolateral plasma membrane vesicles from rat kidney cortex in the presence of CDTA and EGTA as Mg2+- and Ca2+-buffering ligands. ATP hydrolysis is strongly stimulated by Mg2+ with a Km of 13 μ M in the absence or presence of 1 μ M free Ca2+. At free Mg2+ concentrations of 1 μ M and lower, ATP hydrolysis is Mg2+ -independent, but is strongly stimulated by submicromolar Ca2+ concentrations Km = 0.25 μM, Vmax = 24 μmol Pi/h per mg protein). The Ca2+-stimulated ATP hydrolysis strongly decreases at higher Mg2+ concentrations. The Ca2+-stimulated Mg2+-independent ATP hydrolysis is not affected by calmodulin or trifluoperazine and shows no specificity for ATP over ADP, ITP and GTP. In contrast, at high Mg2+ concentrations calmodulin and trifluoperazine affect the high affinity Ca2+-ATPase activity significantly and ATP is the preferred substrate. Control studies on ATP-dependent Ca2+-pumping in renal basolaterals and on Ca2+-ATPase in erythrocyte ghosts suggest that the Ca2+-pumping enzyme requires Mg2+. In contrast, a role of the Ca2+-stimulated Mg2+-independent ATP hydrolysis in active Ca2+ transport across basolateral membranes is rather unlikely. 相似文献
10.
Letizia Albarrán Natalia DionisioEsther López Ginés M. SalidoJuan A. Rosado 《Archives of biochemistry and biophysics》2013
G protein-coupled receptors can be directly modulated by changes in transmembrane voltage in a variety of cell types. Here we show that, while changes in the membrane voltage itself do not induce detectable modifications in the cytosolic Ca2+ concentration, platelet stimulation with thrombin or the PAR-1 and PAR-4 agonist peptides SFLLRN and AYPGKF, respectively, results in Ca2+ release from intracellular stores that is sensitive to the membrane depolarisation. Direct activation of G proteins or phospholipase C by AlF4− and m-3M3FBS, respectively, leads to Ca2+ release that is insensitive to changes in the membrane potential. Thapsigargin-, as well as OAG-induced Ca2+ entry are affected by the membrane voltage, probably as a result of the modification in the driving force for Ca2+ influx; however, hyperpolarisation does not enhance thrombin- or OAG-evoked Ca2+ entry probably revealing the presence of a voltage-sensitive regulatory mechanism. Transmembrane voltage also modulates the activity of the plasma membrane Ca2+-ATPase (PMCA) most likely due to a decrease in the phosphotyrosine content of the pump. Thrombin-stimulated platelet aggregation is modulated by membrane depolarisation by a mechanism that is, at least partially, independent of Ca2+. These observations indicate that PAR-1 and PAR-4 receptors are modulated by the membrane voltage in human platelets. 相似文献
11.
Clayton E. Heyliger Allan R. Prakash John H. McNeill 《Molecular and cellular biochemistry》1989,85(1):75-791
Heart failure is common among the elderly and an alteration in myocardial Ca2+ transport is believed to be involved in its depressed contractile performance. Although ATP-dependent sarcoplasmic reticular (SR) Ca2+ transport has been reported to decrease in old hearts, virtually nothing appears to be known about the Ca2+ pump activity of SR in aging myocardium in the presence of calmodulin, one of its endogenous activators. In this study, the activity of the Ca2+ pump of aging cardiac SR was assessed in the presence of this endogenous stimulator. This assessment was therefore designed to give additional information about the status of this enzyme in old hearts. Male Sprague-Dawley rats were used and were divided into 3 groups: young (4–6 months old); middle-aged (15–17 months old) and old age (24–25 months old). Purified SR membranes were isolated from ventricular tissues. ATP-dependent Ca2+ accumulation by membrane vesicles of middle-aged and old hearts was significantly depressed in comparison to young hearts at all Ca2+ concentrations employed in the absence and presence of calmodulin. The activity of this Ca2+ transporter was similar in middle-aged and old hearts even in the presence of calmodulin. These results suggest that the activity of the Ca2+ pump in SR of aging hearts is depressed even in the presence of calmodulin.C. E. Heyliger is a Scholar of the British Columbia Heart Foundation. 相似文献
12.
13.
Vladimir Parpura Vladimir Grubiši?Alexei Verkhratsky 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》2011,1813(5):984-991
Astrocytes can exocytotically release the gliotransmitter glutamate from vesicular compartments. Increased cytosolic Ca2+ concentration is necessary and sufficient for this process. The predominant source of Ca2+ for exocytosis in astrocytes resides within the endoplasmic reticulum (ER). Inositol 1,4,5-trisphosphate and ryanodine receptors of the ER provide a conduit for the release of Ca2+ to the cytosol. The ER store is (re)filled by the store-specific Ca2+-ATPase. Ultimately, the depleted ER is replenished by Ca2+ which enters from the extracellular space to the cytosol via store-operated Ca2+ entry; the TRPC1 protein has been implicated in this part of the astrocytic exocytotic process. Voltage-gated Ca2+ channels and plasma membrane Na+/Ca2+ exchangers are additional means for cytosolic Ca2+ entry. Cytosolic Ca2+ levels can be modulated by mitochondria, which can take up cytosolic Ca2+ via the Ca2+ uniporter and release Ca2+ into cytosol via the mitochondrial Na+/Ca2+ exchanger, as well as by the formation of the mitochondrial permeability transition pore. The interplay between various Ca2+ sources generates cytosolic Ca2+ dynamics that can drive Ca2+-dependent exocytotic release of glutamate from astrocytes. An understanding of this process in vivo will reveal some of the astrocytic functions in health and disease of the brain. This article is part of a Special Issue entitled: 11th European Symposium on Calcium. 相似文献
14.
Perspective: The List of Potential Volume-sensitive Chloride Currents Continues to Swell (and Shrink)
下载免费PDF全文
![点击此处可从《The Journal of general physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
David E. Clapham 《The Journal of general physiology》1998,111(5):623-624
The channel of the glutamate N-methyl-d-aspartate receptor (NMDAR) transports Ca2+ approximately four times more efficiently than that of Ca2+-permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPAR). To investigate the basis of this difference in these glutamate receptors (GluRs), we measured the ratio of Cs+ efflux and Ca2+ influx in recombinant NMDAR and Ca2+-permeable AMPAR channels expressed in human embryonic kidney 293 (HEK 293) cells over a wide voltage range. At any one potential, this biionic flux ratio was measured by quantifying the total charge and the charge carried by Ca2+ using whole-cell currents and fluorometric techniques (dye overload) with Cs+ internally and Ca2+ externally (1.8 or 10 mM) as the only permeant ions. In AMPAR channels, composed of either GluR-A(Q) or GluR-B(Q) subunits, the biionic flux ratio had a biionic flux-ratio exponent of 1, consistent with the prediction of the Goldman-Hodgkin-Katz current equation. In contrast, for NMDAR channels composed of NR1 and NR2A subunits, the biionic flux-ratio exponent was ∼2, indicating a deviation from Goldman-Hodgkin-Katz. Consistent with these results, in NMDAR channels under biionic conditions with high external Ca2+ and Cs+ as the reference ions, Ca2+ permeability (PCa/PCs) was concentration dependent, being highest around physiological concentrations (1–1.8 mM; PCa/PCs ≈ 6.1) and reduced at both higher (110 mM; PCa/PCs ≈ 2.6) and lower (0.18 mM; PCa/PCs ≈ 2.2) concentrations. PCa/PCs in AMPAR channels was not concentration dependent, being around 1.65 in 0.3–110 mM Ca2+. In AMPAR and NMDAR channels, the Q/R/N site is a critical determinant of Ca2+ permeability. However, mutant AMPAR channels, which had an asparagine substituted at the Q/R site, also showed a biionic flux-ratio exponent of 1 and concentration-independent permeability ratios, indicating that the difference in Ca2+ transport is not due to the amino acid residue located at the Q/R/N site. We suggest that the difference in Ca2+ transport properties between the glutamate receptor subtypes reflects that the pore of NMDAR channels has multiple sites for Ca2+, whereas that of AMPAR channels only a single site. 相似文献
15.
Shmuel Muallem Stephen J. Pandol Timothy G. Beeker 《The Journal of membrane biology》1988,106(1):57-69
Summary
45Ca fluxes and free-cytosolic Ca2+ ([Ca2+]
i
) measurements were used to study the effect of Ca2+-mobilizing hormones on plasma membrane Ca2+ permeability and the plasma membrane Ca2+ pump of pancreatic acinar cells. We showed before (Pandol, S.J., et al., 1987.J. Biol. Chem.
262:16963–16968) that hormone stimulation of pancreatic acinar cells activated a plasma membrane Ca2+ entry pathway, which remains activated for as long as the intracellular stores are not loaded with Ca2+. In the present study, we show that activation of this pathway increases the plasma membrane Ca2+ permeability by approximately sevenfold. Despite that, the cells reduce [Ca2+]i back to near resting levels. To compensate for the increased plasma membrane Ca2+ permeability, a plasma membrane Ca2+ efflux mechanism is also activated by the hormones. This mechanism is likely to be the plasma membrane Ca2+ pump. Activation of the plasma membrane Ca2+ pump by the hormones is time dependent and 1.5–2 min of cell stimulation are required for maximal Ca2+ pump activation. From the effect of protein kinase inhibitors on hormone-mediated activation of the pump and the effect of the phorbol ester 12-0-tetradecanoyl phorbol, 13-acetate (TPA) on plasma membrane Ca+ efflux, it is suggested that stimulation of protein kinase C is required for the hormone-dependent activation of the plasma membrane Ca2+ pump. 相似文献
16.
Summary
86Rb+ fluxes have been measured in suspensions of vesicles prepared from the epithelium of toad urinary bladder. A readily measurable barium-sensitive, ouabain-insensitive component has been identified; the concentration of external Ba2+ required for half-maximal inhibition was 0.6mm. The effects of externally added cations on86Rb+ influx and efflux have established that this pathway is conductive, with a selectivity for K+, Rb+ and Cs+ over Na+ and Li+. the Rb+ uptake is inversely dependent on external pH, but not significantly affected by internal Ca2+ or external amiloride, quinine, quinidine or lidocaine. It is likely, albeit not yet certain, that the conductive Rb+ pathway is incorporated in basolateral vesicles oriented right-side-out. It is also not yet clear whether this pathway comprises the principle basolateral K+ channel in vivo, and that its properties have been unchanged during the preparative procedures. Subject to these caveats, the data suggest that the inhibition by quinidine of Na+ transport across toad bladder does not arise primarily from membrane depolarization produced by a direct blockage of the basolateral channels. It now seems more likely that the quinidine-induced elevation of intracellular Ca2+ activity directly blocks apical Na+ entry. 相似文献
17.
Mauro Salvi 《生物化学与生物物理学报:生物膜》2004,1661(2):113-124
Mammalian mitochondria are able to enhance Ca2+ accumulation in the presence of polyamines by activating the saturable systems of Ca2+ inward transport and buffering extramitochondrial Ca2+ concentrations to levels similar to those in the cytosol of resting cells. This effect renders them responsive to regulate free Ca2+ concentrations in the physioloical range. The mechanism involved is due to a rise in the affinity of the Ca2+ transport system, induced by polyamines, most probably exhibiting allosteric behaviour. The regulatory site of this mechanism is the so-called S1 binding site of polyamines, which operates in physiological conditions and is located in the energy well between the two peaks present in the energy profile of mitochondrial spermine transport. Spermine is bidirectionally transported across teh inner membrane by cycling, in which influx and efflux are driven by electrical and pH gradients, respectively. Most probably, polyamine affects the Ca2+ transport system when it acts from the outside-that is, in the direction of its uniporter channel, in order to reach the S1 site. Important physiological functions are related to activation of Ca2+ transport systems by polyamines and their interactions with the S1 site. These functions include a rise in the metabolic rate for energy supply and modulation of mitochondrial permeability transition induction, with consequent effects on the triggering of the apoptotic pathway. 相似文献
18.
Rita Sikdar Uma Ganguly Sucheta Chandra Gautam Adhikary Parimal C. Sen 《Journal of biosciences》1993,18(1):73-82
Microsomal membrane vesicles isolated from goat spermatozoa contain Ca2+-ATPase, and exhibit Ca2+ transport activities that do not require exogenous Mg2+ .The enzyme activity is inhibited by calcium-channel inhibitors,e.g. verapamil and diltiazem, like the well known Ca2+ , Mg2+-ATPase. The uptake of calcium is ATP (energy)-dependent and the accumulated Ca2+ can be completely released by the Ca2+ ionophore A23187, suggesting that a significant fraction of the vesicles are oriented inside out 相似文献
19.
Effects of endotoxin administration on the ATP-dependent Ca2+ transport in canine cardiac sarcolemma were investigated. The results show that the sidedness of the sarcolemmal vesicles was not affected but the ATP-dependent Ca2+ transport in cardiac sarcolemma was decreased by 22 to 46% (p < 0.05) at 4 h following endotoxin administration. The kinetic analysis indicates that the Vmax for ATP and for Ca2+ were decreased by 50% (p < 0.01) and 32% (p < 0.01), respectively, while the Km values for ATP and Ca2+ were not significantly affected after endotoxin administration. Magnesium (1–5 mM) stimulated while vanadate (0.25–3.0 M) inhibited the ATP-dependent Ca2+ transport, but the Mg2+-stimulated and the vanadate-inhibitable activities remained significantly lower in the endotoxin-treated animals. These data demonstrate that endotoxin administration impairs the ATP-dependent Ca2+ transport in canine cardiac sarcolemma and that the impairment is associated with a mechanism not affecting the affinity towards ATP and Ca2+. Additional experiments show that the Ca2+ sensitivity of the Ca2+-ATPase activity was indifferent between the control and endotoxic groups suggesting that endotoxic injury impairs Ca2+ pumping without affecting Ca2+-ATPase activity. Since sarcolemmal ATP-dependent Ca2+ transport plays an important role in the regulation of cytosolic Ca2+ homeostasis, an impairment in the sarcolemmal ATP-dependent Ca2+ transport induced by endotoxin administration may have a pathophysiological significance in contributing to the development of myocardial dysfunction in endotoxin shock. 相似文献
20.
Inesi G 《Journal of cell communication and signaling》2011,5(3):227-237
The calcium transport ATPase and the copper transport ATPase are members of the P-ATPase family and retain an analogous catalytic
mechanism for ATP utilization, including intermediate phosphoryl transfer to a conserved aspartyl residue, vectorial displacement
of bound cation, and final hydrolytic cleavage of Pi. Both ATPases undergo protein conformational changes concomitant with
catalytic events. Yet, the two ATPases are prototypes of different features with regard to transduction and signaling mechanisms.
The calcium ATPase resides stably on membranes delimiting cellular compartments, acquires free Ca2+ with high affinity on one side of the membrane, and releases the bound Ca2+ on the other side of the membrane to yield a high free Ca2+ gradient. These features are a basic requirement for cellular Ca2+ signaling mechanisms. On the other hand, the copper ATPase acquires copper through exchange with donor proteins, and undergoes
intracellular trafficking to deliver copper to acceptor proteins. In addition to the cation transport site and the conserved
aspartate undergoing catalytic phosphorylation, the copper ATPase has copper binding regulatory sites on a unique N-terminal
protein extension, and has also serine residues undergoing kinase assisted phosphorylation. These additional features are
involved in the mechanism of copper ATPase intracellular trafficking which is required to deliver copper to plasma membranes
for extrusion, and to the trans-Golgi network for incorporation into metalloproteins. Isoform specific glyocosylation contributes
to stabilization of ATP7A copper ATPase in plasma membranes. 相似文献