共查询到20条相似文献,搜索用时 390 毫秒
1.
Enn K. Seppet Frantisek Kolar Ian M. C. Dixon Tomoji Hata Naranjan S. Dhalla 《Molecular and cellular biochemistry》1993,129(2):145-159
In order to examine the regulatory role of thyroid hormone on sarcolemmal Ca2+-channels, Na+–Ca2+ exchange and Ca2+-pump as well as heart function, the effects of hypothyroidism and hyperthyroidism on rat heart performance and sarcolemmal Ca2+-handling were studied. Hyperthyroid rats showed higher values for heart rate (HR), maximal rates of ventricular pressure development+(dP/dt)max and pressure fall–(dP/dt)max, but shorter time to peak ventricular pressure (TPVP) and contraction time (CT) when compared with euthyroid rats. The left ventricular systolic pressure (LVSP) and left ventricular end-diastolic pressure (LVEDP), as well as aortic systolic and diastolic pressures (ASP and ADP, respectively) were not significantly altered. Hypothyroid rats exhibited decreased values of LVSP, HR, ASP, ADP, +(dP/dt)max and –(dP/dt)max but higher CT when compared with euthyroid rats; the values of LVEDP and TPVP were not changed. Studies with isolated-perfused hearts showed that while hypothyroidism did not modulate the inotropic response to extracellular Ca2+ and Ca2+ channel blocker verapamil, hyperthyroidism increased sensitivity to Ca2+ and decreased sensitivity to verapamil in comparison to euthyroid hearts. Studies of [3H]-nitrendipine binding with purified cardiac sarcolemmal membrane revealed decreased number of high affinity binding sites (Bmax) without any change in the dissociation constant for receptor-ligand complex (Kd) in the hyperthyroid group when compared with euthyroid sarcolemma; hypothyroidism had no effect on these parameters. The activities of sarcolemmal Ca2+-stimulated ATPase, ATP-dependent Ca2+ uptake and ouabain-sensitive Na+–K+ ATPase were decreased whereas the Mg2+-ATPase activity was increased in hypothyroid hearts. On the other hand, sarcolemmal membranes from hyperthyroid samples exhibited increased ouabain-sensitive Na+–K+ ATPase activity, whereas Ca2+-stimulated ATPase, ATP-dependent Ca2+ uptake, and Mg2+-ATPase activities were unchanged. The Vmax and Ka for Ca2+ of cardiac sarcolemmal Na+–Ca2+ exchange were not altered in both hyperthyroid and hypothyroid states. These results indicate that the status of sarcolemmal Ca2+-transport processes is regulated by thyroid hormones and the modification of Ca2+-fluxes across the sarcolemmal membrane may play a crucial role in the development of thyroid state-dependent contractile changes in the heart. 相似文献
2.
Naranjan S. Dhalla Vincenzo Panagia Naoki Makino Robert E. Beamish 《Molecular and cellular biochemistry》1988,82(1-2):75-79
In order to identify defects in Na+-Ca2+ exchange and Ca2+-pump systems in cardiomyopathic hearts, the activities of sarcolemmal Na+-dependent Ca2+ uptake, Na+-induced Ca2+ release, ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase were examined by employing cardiomyopathic hamsters (UM-X7.1) and catecholamine-induced cardiomyopathy produced by injecting isoproterenol into rats. The rates of Na+-dependent Ca2+ uptake, ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase activities of sarcolemmal vesicles from genetically-linked cardiomyopathic as well as catecholamine-induced cardiomyopathic hearts were decreased without any changes in Na+-induced Ca2+-release. Similar results were obtained in Ca2+-paradox when isolated rat hearts were perfused for 5 min with a medium containing 1.25 mM Ca2+ following a 5 min perfusion with Ca2+-free medium. Although a 2 min reperfusion of the Ca2+-free perfused hearts depressed sarcolemmal Ca2+-pump activities without any changes in Na+-induced Ca2+-release, Na+-dependent Ca2+ uptake was increased. These results indicate that alterations in the sarcolemmal Ca2+-efflux mechanisms may play an important role in cardiomyopathies associated with the development of intracellular Ca2+ overload. 相似文献
3.
K.Damodar Reddy A Chaudhuri K Thangavelu 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》1997,116(4):459-466
Tissue-specific age-dependent changes were observed in Na+K+-, Ca2+-, and Mg2+-ATPase activities in tropical tasar silkworm, Antheraea mylitta Drury. Maximum enzyme activity was recorded in all the tissues on day 12 (before spinning) in control group of animals. In testis, Na+K+-, Ca2+-, and Mg2+-ATPase activities gradually increased from day 2 to day 12 during fifth larval age and level was maintained up to adult eclosion while, in ovary, a marked decline was noted up to day of adult emergence. Further, a significant and sharp rise was found in ATPase activity in silk gland tissue up to day 12 and afterwards a drastic fall was noted on day 15 (end of spinning) during fifth larval age.Administration of T4 to fifth stage larvae (1 hr old) at doses 0.5–2.0 μg/g significantly elevated the Na+K+-, Ca2+-, and Mg2+-ATPase activities in larval and pupal gonads in a dose-dependent fashion. But, in moths, the enhancement was very much confined to Na+K+- and Ca2+-ATPase in testes and only Ca2+-ATPase in ovaries. Again, in silk glands thyroxine (0.5–2.0 μg/g) caused a significant rise in the all ion-dependent ATPase activities only during the fifth larval stage. Interestingly, higher doses of T4 (4.0 μg/g) caused a significant reduction in Na+K+-, Ca2+- and Mg2+-ATPase in all the tissues almost all the days studied so far. However, lower doses of T4 (0.1 and 0.25 μg/g) remained ineffective in altering the different ion-specific ATPase activities. This study suggests, that mammalian thyroxine has a metabolic influence showing biphasic nature of action in tasar silkworm ATPase system. 相似文献
4.
Regulation of the Na+/K+-ATPase by insulin: Why and how? 总被引:4,自引:0,他引:4
The sodium-potassium ATPase (Na+/K+-ATPase or Na+/K+-pump) is an enzyme present at the surface of all eukaryotic cells, which actively extrudes Na+ from cells in exchange for K+ at a ratio of 3:2, respectively. Its activity also provides the driving force for secondary active transport of solutes such as amino acids, phosphate, vitamins and, in epithelial cells, glucose. The enzyme consists of two subunits ( and ) each expressed in several isoforms. Many hormones regulate Na+/K+ -ATPase activity and in this review we will focus on the effects of insulin. The possible mechanisms whereby insulin controls Na+/K+-ATPase activity are discussed. These are tissue- and isoform-specific, and include reversible covalent modification of catalytic subunits, activation by a rise in intracellular Na+ concentration, altered Na+ sensitivity and changes in subunit gene or protein expression. Given the recent escalation in knowledge of insulin-stimulated signal transduction systems, it is pertinent to ask which intracellular signalling pathways are utilized by insulin in controlling Na+/K+-ATPase activity. Evidence for and against a role for the phosphatidylinositol-3-kinase and mitogen activated protein kinase arms of the insulin-stimulated intracellular signalling networks is suggested. Finally, the clinical relevance of Na+/K+-ATPase control by insulin in diabetes and related disorders is addressed. 相似文献
5.
In this review we summarize mutagenesis work on the structure–function relationship of transmembrane segment M1 in the Na+,K+-ATPase and the sarco(endo)plasmic reticulum Ca2+-ATPase. The original hypothesis that charged residues in the N-terminal part of M1 interact with the transported cations
can be rejected. On the other hand hydrophobic residues in the middle part of M1 turned out to play crucial roles in Ca2+ interaction/occlusion in Ca2+-ATPase and K+ interaction/occlusion in Na+,K+-ATPase. Leu65 of the Ca2+-ATPase and Leu99 of the Na+,K+-ATPase, located at homologous positions in M1, function as gate-locking residues that restrict the mobility of the side chain
of the cation binding/gating residue of transmembrane segment M4, Glu309/Glu329. A pivot formed between a pair of a glycine and a bulky residue in M1 and M3 seems critical to the opening of the extracytoplasmic
gate in both the Ca2+-ATPase and the Na+,K+-ATPase.
All numbering of Na+,K+-ATPase amino acid residues in this article refers to the sequence of the rat α1-isoform. 相似文献
6.
Theo J. M. Schoenmakers Peter H. M. Klaren Gert Flik Robert A. C. Lock Peter K. T. Pang Sjoerd E. Wendelaar Bonga 《The Journal of membrane biology》1992,127(3):161-172
Summary The inhibition of Ca2–-ATPase, (Na++K+)-ATPase and Na+/Ca2+ exchange by Cd2+ was studied in fish intestinal basolateral plasma membrane preparations. ATP driven 45Ca2+ uptake into inside-out membrane vesicles displayed a K
m
for Ca2+ of 88±17 nm, and was extremely sensitive to Cd2+ with an IC50 of 8.2±3.0 pM Cd2+, indicating an inhibition via the Ca2+ site. (Na++K+)-ATPase activity was half-maximally inhibited by micromolar amounts of Cd2+, displaying an IC50 of 2.6±0.6 m Cd2+. Cd2+ ions apparently compete for the Mg2+ site of the (Na– +K+)-ATPase. The Na+/Ca2+ exchanger was inhibited by Cd2+ with an IC50 of 73±11 nm. Cd2+ is a competitive inhibitor of the exchanger via an interaction with the Ca2+ site (K
i
= 11 nm). Bepridil, a Na+ site specific inhibitor of Na+/Ca2+ exchange, induced an additional inhibition, but did not change the K
i
of Cd2+. Also, Cd2+ is exchanged against Ca2+, albeit to a lesser extent than Ca2+. The exchanger is only partly blocked by the binding of Cd2+. In vivo cadmium that has entered the enterocyte may be shuttled across the basolateral plasma membrane by the Na+/Ca2+ exchanger. We conclude that intracellular Cd2+ ions will inhibit plasma membrane proteins predominantly via a specific interaction with divalent metal ion sites.We would like to thank Dr. D. Fackre (University of Alberta, Canada) for stimulating discussions and Mr. F.A.T. Spanings (University of Nijmegen, The Netherlands) for excellent fish husbandry. The fura-2 measurements of intracellular Ca2+ concentrations in tilapia enterocytes were carried out in the Department of Physiology, School of Medicine, University of Alberta, Edmonton, Alberta T6G 2H7, Canada. Th.J.M. Schoenmakers and G. Flik were supported by travel grants from the Foundation for Fundamental Biological Research (BION) and the Netherlands Organization for Scientific Research (NWO). 相似文献
7.
W. H. M. Peters A. G. H. Ederveen M. H. L. Salden J. J. H. H. M. de Pont S. L. Bonting 《Journal of bioenergetics and biomembranes》1984,16(3):223-232
Goat antisera against (Na+ + K+)-ATPase and its isolated subunits and against (K+ + H+)-ATPase have been prepared in order to test for immune cross-reactivity between the two enzymes, whose catalytic subunits show great chemical similarity. None of the (Na+ + K+)-ATPase antisera cross-reacted with (K+ + H+)-ATPase or inhibited its enzyme activity. The same was true for the (K+ + H+)-ATPase antiserum with regard to (Na+ + K+)-ATPase and its subunits and its enzyme activity. So not withstanding the chemical similarity of their subunits, there is no immunological cross-reactivity between these two plasma membrane ATPases.Number LIII in the series Studies on (Na+ + K+)-Activated ATPase. 相似文献
8.
Although in vitro studies have shown that oxygen free radicals depress the sarcolemmal Ca2+-pump activity and thereby may cause the occurrence of intracellular Ca2+ overload for the genesis of contractile failure, the exact relationship between changes in sarcolemmal Ca2+-pump activity and cardiac function due to these radicals is not clear. In this study we examined the effects of oxygen radicals on sarcolemmal Ca2+ uptake and Ca2+-stimulated ATPase activities as well as contractile force development by employing isolated rat heart preparations. When hearts were perfused with medium containing xanthine plus xanthine oxidase, the sarcolemmal Ca2+-stimulated ATPase activity and ATP-dependent Ca2+ accumulation were depressed within 1 min whereas the developed contractile force, rate of contraction and rate of relaxation were increased at 1 min and decreased over 3–20 min of perfusion. The resting tension started increasing at 2 min of perfusion with xanthine plus xanthine oxidase. Catalase showed protective effects against these alterations in heart function and sarcolemmal Ca2+-pump activities upon perfusion with xanthine plus xanthine oxidase whereas superoxide dismutase did not exert such effects. The combination of catalase and superoxide dismutase did not produce greater effects in comparison to catalase alone. These results are consistent with the view that the depression of heart sarcolemmal Ca2+ pump activities may result in myocardial dysfunction due to the formation of hydrogen peroxide and/or hydroxyl radicals upon perfusing the hearts with xanthine plus xanthine oxidase. 相似文献
9.
Plasma membrane (PM) Na+, K+-ATPase, plays crucial roles in numerous physiological processes. Cardiac steroids (CS), such as ouabain and bufalin, specifically bind to the Na+, K+-ATPase and affect ionic homeostasis, signal transduction, and endocytosed membrane traffic. CS-like compounds, synthesized in and released from the adrenal gland, are considered a new family of steroid hormones. Previous studies showed that ouabain induces slow Ca2+ oscillations in COS-7 cells by enhancing the interactions between Na+, K+-ATPase, inositol 1,4,5-trisphosphate receptor (IP3R) and Ankyrin B (Ank-B) to form a Ca2+ signaling micro-domain. The activation of this micro-domain, however, is independent of InsP3 generation. Thus, the mechanism underlying the induction of these slow Ca2+ oscillations remained largely unclear. We now show that other CS, such as bufalin, can also induce Ca2+ oscillations. These oscillations depend on extracellular Ca2+ concentrations [Ca2+]out and are inhibited by Ni2+. Furthermore, we found that these slow oscillations are Na+out dependent, abolished by Na+/Ca2+ exchanger1 (NCX1)-specific inhibitors and markedly attenuated by NCX1 siRNA knockdown. Based on these results, a model is presented for the CS-induced slow Ca2+ oscillations in COS-7 cells. 相似文献
10.
Danijela Krstić Katarina Krinulović Vesna Vasić 《Journal of enzyme inhibition and medicinal chemistry》2013,28(5):469-476
Kinetics and inhibition of Na+/K+-ATPase and Mg2+-ATPase activity from rat synaptic plasma membrane (SPM), by separate and simultaneous exposure to transition (Cu2+, Zn2+, Fe2+ and.Co2+) and heavy metals (Hg2+and Pb2+) ions were studied. All investigated metals produced a larger maximum inhibition of Na+/K+-ATPase than Mg2+-ATPase activity. The free concentrations of the key species (inhibitor, MgATP2 ? , MeATP2 ? ) in the medium assay were calculated and discussed. Simultaneous exposure to the combinations Cu2+/Fe2+ or Hg2+/Pb2+caused additive inhibition, while Cu2+/Zn2+ or Fe2+/Zn2+ inhibited Na+/K+-ATPase activity synergistically (i.e., greater than the sum metal-induced inhibition assayed separately). Simultaneous exposure to Cu2+/Fe2+ or Cu2+/Zn2+ inhibited Mg2+-ATPase activity synergistically, while Hg2+/Pb2+ or Fe2+/Zn2+ induced antagonistic inhibition of this enzyme. Kinetic analysis showed that all investigated metals inhibited Na+/K+-ATPase activity by reducing the maximum velocities (Vmax) rather than the apparent affinity (Km) for substrate MgATP2-, implying the noncompetitive nature of the inhibition. The incomplete inhibition of Mg2+-ATPase activity by Zn2+, Fe2+ and Co2+ as well as kinetic analysis indicated two distinct Mg2+-ATPase subtypes activated in the presence of low and high MgATP2 ? concentration. EDTA, L-cysteine and gluthathione (GSH) prevented metal ion-induced inhibition of Na+/K+-ATPase with various potencies. Furthermore, these ligands also reversed Na+/K+-ATPase activity inhibited by transition metals in a concentration-dependent manner, but a recovery effect by any ligand on Hg2+-induced inhibition was not obtained. 相似文献
11.
Previous studies in chick embryo cardiac myocytes have shown that the inhibition of Na+/K+-ATPase with ouabain induces cell shrinkage in an isosmotic environment (290 mOsm). The same inhibition produces an enhanced RVD (regulatory volume decrease) in hyposmotic conditions (100 mOsm). It is also known that submitting chick embryo cardiomyocytes to a hyperosmotic solution induces shrinkage and a concurrent intracellular alkalization. The objective of this study was to evaluate the involvement of intracellular pH (pHi), intracellular Ca2+ ([Ca2+]i) and Na+/K+-ATPase inhibition during hyposmotic swelling. Changes in intracellular pH and Ca2+ were monitored using BCECF and fura-2, respectively. The addition of ouabain (100 M) under both isosmotic and hyposmotic stimuli resulted in a large increase in [Ca2+]i (200%). A decrease in pHi (from 7.3 ± 0.09 to 6.4 ± 0.08, n = 6; p < 0.05) was only observed when ouabain was applied during hyposmotic swelling. This acidification was prevented by the removal of extracellular Ca2+. Inhibition of Na+/H2+ exchange with amiloride (1 mM) had no effect on the ouabain-induced acidification. Preventing the mitochondrial accumulation of Ca2+ using CCCP (10 M) resulted in a blockade of the progressive acidification normally induced by ouabain. The inhibition of mitochondrial membrane K+/H+ exchange with DCCD (1 mM) also completely prevented the acidification. Our results suggest that intracellular acidification upon cell swelling is mediated by an initial Ca2+ influx via Na+/Ca2+ exchange, which under hyposmotic conditions activates the K+ and Ca2+ mitochondrial exchange systems (K+/H+ and Ca2+/H+).Deceased 相似文献
12.
B.S. Jena B.K. Patnaik 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》1995,111(4):545-552
Hepatic Na+-K+-ATPase and Mg2+-ATPase activities of male green lizards declined during the maturation phase (juvenile to 1-year-old) and stabilized thereafter. On the other hand, the Ca2+-ATPase activity of the liver declined during the later half of the life span (1-year-old to 2–4-year-old). Starvation stress induced a decline in hepatic Na+-K+-ATPase and Mg2+-ATPase activities of juvenile lizards and caused an increase in 1-year-old and 2–4-year-old counterparts. The Ca2+-ATPase activity declined only in starved 1-year-old lizards. Following cold stress, the hepatic Na+-K+-ATPase activity of juvenile lizards showed a higher degree of decline than 2–4-year-old counterparts. The Mg2+-ATPase activity declined in cold-stressed juvenile lizards, but the parameter was elevated in similarly treated 1-year-old lizards. On the other hand, the increase in Ca2+-ATPase activity in response to cold stress was confined only to 2–4-year-old lizards. 相似文献
13.
- 1. 1. The Mg2+- plus Ca2+-dependent ATPase (Ca2+-ATPase) in human red cell membranes is susceptible to inhibition by low concentrations of vanadate.
- 2. 2. Several natural activators of Ca2+-ATPase (Mg2+, K+, Na+ and calmodulin) modify inhibition by increasing the apparent affinity of the enzyme for vanadate.
- 3. 3. Among the ligands tested, K+, in combination with Mg2+, had the most pronounced effect on inhibition by vanadate.
- 4. 4. Under conditions optimal for inhibition of Ca2+-ATPase, the K
for vanadate was 1.5 μM and inhibition was nearly complete at saturating vanadate concentrations.
- 5. 5. There are similarities between the kinetics of inhibition of red cell Ca2+-ATPase and (Na+ + K+)-ATPase prepared from a variety of sources; however, (Na+ + K+)-ATPase is approx. 3 times more sensitive to inhibition by vanadate.
Keywords: Ca2+-ATPase; Red cell membrane; Vanadate; Calmodulin 相似文献
14.
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
15.
Shalini Gulati Madhu Khullar Ramandeep Singh Savita Kumari N. K. Ganguly B. K. Sharma 《Journal of biosciences》1999,24(1):59-67
A humoral ouabain-like plasma factor has been observed in patients with essential hypertension (EHT). In the present study,
we hypothesized that this humoral factor might be responsible for the elevated cytosolic free calcium concentrations [Ca2+]i seen in these patients. Patients with mild to moderate EHT and their normotensive first degree blood relatives (NTBR) participated
in the study. Platelet Na+, K+-ATPase activity was assayed in EHT patients and their NT first-degree relatives. To confirm the ouabain-like activity in
plasma from EHT patients, control platelets were incubated with EHT and NTBR plasma and their Na+, K+-ATPase activity was measured. In addition, the effect of EHT plasma on platelet45Ca-uptake was studied. Thein vitro effects of ouabain (10 ΜM) on (i)45Ca-uptake and (ii) [Ca2+]i response in control platelets were also observed. A decreased Na+K+-ATPase activity (P< 0.05) was observed in platelet membranes from EHT patients. Incubation of control platelets with EHT plasma decreased their
Na+, K+-ATPase activity (P< 0.01) and increased their45Ca-uptake (P< 0.05). C-18 Sep-Pak filtered hypertensive plasma extracts (containing the ouabain-like fraction) also decreased Na+, K+-ATPase activity (P< 001) in control platelet membranes.In vitro incubation of control platelets with ouabain increased45Ca-uptake (P< 005) and [Ca2+]i response (P< 0.05) in these platelets. Thus it appears that an ouabain-like factor in the EHT plasma may contribute to the elevated platelet
[Ca2+]i observed in EHT patients. 相似文献
16.
Erythrocyte plasma membranes of non-insulin dependent diabetic humans (NIDDM) and healthy humans were prepared by hypotonic lysis. The specific activity of (Na+–K+)-ATPase of NIDDM membranes, both in the absence and presence of digoxin were lower than the specific activity of normal enzymes (83.6 percent and 74.0 percent of the normal enzyme respectively). Addition of digoxin decreased the activity of this enzyme (38.0 percent in NIDDM and 30.0 percent in normal enzyme).Although the affinity of the pump for ATP was similar in both membranes of NIDDM and normal humans (Km for ATP=19.9±0.24M ATP and 20.0±0.21 M ATP respectively), the Vmax of NIDDM membranes was more than 20 percent lower than that of the normal enzyme. The specific activity of Mg2+-dependent Ca2+-pumping ATPase (Ca2+–Mg2+)-ATPase) of NIDDM membrane was lower than 80 percent of the specific activity of the normal enzymes. While the affinity of the pump for ATP was lower in the membranes of NIDDM (Km for ATP=50.0±4.3 M ATP) in comparison to normal membranes (Km for ATP=63.1±38M ATP), the Vmax of NIDDM membranes was similar to the normal enzyme. Altogether, these findings suggest that both the (Na+–K+)-ATPase and Ca2+-pumping ATPase of NIDDM membranes are less functional than the enzymes in normal erythrocytes. 相似文献
17.
Streck EL Zugno AI Tagliari B Franzon R Wannmacher CM Wajner M Wyse AT 《Neurochemical research》2001,26(11):1195-1200
The objective of the present study was to investigate the effects of preincubation of hippocampus homogenates in the presence of homocysteine or methionine on Na+, K+-ATPase and Mg2+-ATPase activities in synaptic membranes of rats. Homocysteine significantly inhibited Na+, K+-ATPase activity, whereas methionine had no effect. Mg2+-ATPase activity was not altered by the metabolites. We also evaluated the effect of incubating glutathione, cysteine, dithiothreitol, trolox, superoxide dismutase and GM1 ganglioside alone or incubation with homocysteine on Na+, K+-ATPase activity. Tested compounds did not alter Na+, K+-ATPase and Mg2+-ATPase activities, but except for trolox, prevented the inhibitory effect of homocysteine on Na+, K+-ATPase activity. These results suggest that inhibition of this enzyme activity by homocysteine is possibly mediated by free radicals and may contribute to the neurological dysfunction found in homocystinuric patients. 相似文献
18.
Changes in protoporphyrin conformation, partial pressures of O2 and CO2, and the mechanisms responsible for regulation of pCa and pH in erythrocytes were studied in essential hypertension (EH). Changes in protoporphyrin conformation in EH were accompanied by a decrease in the partial pressure of O2 and an increase in the partial pressure of CO2. This was associated with increased activities of Na+/H+-exchange and Ca2+-dependent K+-channels and with a decreased activity of Ca2+-ATPase. The changes in protoporphyrin conformation in EH are suggested to decrease the efficiency of O2 metabolism in hemoglobin and increase the values of intracellular pCa and pH of erythrocytes. 相似文献
19.
Rat C6 glioma cells were cultured for 4 days in MEM medium supplemented with 10% bovine serum and Na+,K+-ATPase activity was determined in homogenates of harvested cells. Approximately 50% of enzyme activity was attained at 1.5 mM K+ and the maximum (2.76±0.13 mol Pi/h/mg protein) at 5 mM K+. The specific activity of Na+,K+-ATPase was not influenced by freezing the homogenates or cell suspensions before the enzyme assay. Ten minutes' exposure of glioma cells to 10–4 or 10–5 M noradrenaline (NA) remained without any effect on NA+,K+-ATPase activity. Neither did the presence of NA in the incubation medium, during the enzyme assay, influence the enzyme activity. The nonresponsiveness of Na+,K+-ATPase of C6 glioma cells to NA is consistent with the assumption that (+) form of the enzyme may be preferentially sensitive to noradrenaline. Na+,K+-ATPase was inhibited in a dose-dependent manner by vanadate and 50% inhibition was achieved at 2×10–7 M concentration. In spite of the fact that Na+,K+-ATPase of glioma cells was not responsive to NA, the latter could at least partially reverse vanadate-induced inhibition of the enzyme. Although the present results concern transformed glial cells, they suggest the possibility that inhibition of glial Na+,K+-ATPase may contribute to the previously reported inhibition by vanadate of Na+,K+-ATPase of the whole brain tissue. 相似文献
20.
- 1. (1) VO3− combines with high affinity to the Ca2+-ATPase and fully inhibits Ca2+-ATPase and Ca2+-phosphatase activities. Inhibition is associated with a parallel decrease in the steady-state level of the Ca2+-dependent phosphoenzyme.
- 2. (2) VO3− blocks hydrolysis of ATP at the catalytic site. The sites for VO3− also exhibit negative interactions in affinity with the regulatory sites for ATP of the Ca2+-ATPase.
- 3. (3) The sites for VO3− show positive interactions in affinity with sites for Mg2+ and K+. This accounts for the dependence on Mg2+ and K+ of the inhibition by VO3−. Although, with less effectiveness, Na+ substitutes for K+ whereas Li+ does not. The apparent affinities for Mg2+ and K+ for inhibition by VO3− seem to be less than those for activation of the Ca2+-ATPase.
- 4. (4) Inhibition by VO3− is independent of Ca2+ at concentrations up to 50 μM. Higher concentrations of Ca2+ lead to a progressive release of the inhibitory effect of VO3−.
Keywords: Ca2+-ATPase; Vanadate inhibition; K+; Li+; (Red cell membrane) 相似文献