Role of platelet plasma membrane Ca^(2+)-ATPase in health and disease

Platelets have essential roles in both health and disease. Normal platelet function is required for hemostasis.Inhibition of platelet function in disease or by pharmacological treatment results in bleeding disorders.On the other hand,hyperactive platelets lead to heart attack and stroke.Calcium is a major second messenger in platelet activation,and elevated intracellular calcium leads to hyperactive platelets.Elevated platelet calcium has been documented in hypertension and diabetes;both conditions increase the likelihood of heart attack and stroke. Thus,proper regulation of calcium metabolism in the platelet is extremely important.Plasma membrane Ca2+-ATPase(PMCA)is a major player in platelet calcium metabolism since it provides the only significant route for calcium efflux.In keeping with the important role of calcium in platelet function,PMCA is a highly regulated transporter.In human platelets,PMCA is activated by Ca2+/calmodulin,by cAMP-dependent phosphorylation and by calpain-dependent removal of the inhibitory peptide.It is inhibited by tyrosine phosphorylation and calpain-dependent proteolysis.In addition,the cellular location of PMCA is regulated by a PDZ-domain-dependent interaction with the cytoskeleton during platelet activation.Rapid regulation by phosphorylation results in changes in the rate of platelet activation,whereas calpain-dependent proteolysis and interaction with the cytoskeleton appears to regulate later events such as clot retraction.In hypertension and diabetes,PMCA expression is upregulated while activity is decreased, presumably due to tyrosine phosphorylation.Clearly,a more complete understanding of PMCA function in human platelets could result in the identification of new ways to control platelet function in disease states.

Plasma membrane Ca^(2+)-ATPases:Targets of oxidative stress in brain aging and neurodegeneration

The plasma membrane Ca2+-ATPase(PMCA)pumps play an important role in the maintenance of precise levels of intracellular Ca2+[Ca2+]i,essential to the functioning of neurons.In this article,we review evidence showing age-related changes of the PMCAs in synaptic plasma membranes(SPMs).PMCA activity and protein levels in SPMs diminish progressively with increasing age. The PMCAs are very sensitive to oxidative stress and undergo functional and structural changes when exposed to oxidants of physiological relevance.The major signatures of oxidative modification in the PMCAs are rapid inactivation,conformational changes,aggregation, internalization from the plasma membrane and proteolytic degradation.PMCA proteolysis appears to be mediated by both calpains and caspases.The predominance of one proteolytic pathway vs the other,the ensuing pattern of PMCA degradation and its consequence on pump activity depends largely on the type of insult,its intensity and duration.Experimental reduction of PMCA expression not only alters the dynamics of cellular Ca2+ handling but also has a myriad of downstream conse-quences on various aspects of cell function,indicating a broad role of these pumps.Age-and oxidation-related down-regulation of the PMCAs may play an important role in compromised neuronal function in the aging brain and its several-fold increased susceptibility to neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease,and stroke.Therapeutic approaches that protect the PMCAs and stabilize[Ca2+]i homeostasis may be capable of slowing and/or preventing neuronal degeneration.The PMCAs are therefore emerging as a new class of drug targets for therapeutic interventions in various chronic degenerative disorders.

The investigation for the relationship among serum leptin, erythrocyte membrane Ca^(2+)-ATPase activity and hypertensive disorder complicating pregnancy

Objective： To study the significance of Leptin and the activity of erythrocyte membrane Ca^2＋-ATPase（EMCA） in the development of hypertensive disorder complicating pregnancy. Methods： Radioimmunoassay was used to test the level of serum Leptin, and the activity of EMCA was determined chemically in 38 pregnant women with hypertensive disorder complicating pregnancy and 36 normotensive pregnant women. Results： The level of serum Leptin in hypertensive disorder complicating pregnancy（gestational hypertension： 13.76 ± 3.46 ng/ml; preeclampsia： 15.76 ± 5.47 ng/ml; eclampsia： 18.32 ± 6.38 ng/ml）was significantly higher than that in normotensive pregnant women （11.33 ± 2.93 ng/ml） ,respectively. The average EMCA activity of patients with hypertensive disorder complicating pregnancy （gestational hypertension： 1.65 ± 0.24 μmol·pi/mg.h ; preeclampsia： 1.37 ± 0.19 μ mol·pi/mg·h;eclampsia：1.12 ± 0.14 μmol·pi/mg·h） was significantly lower than that of normotensive pregnant women（1.83 ± 0.38 μ mol·pi/mg·h）,respectively. There was a negative correlation between the level of serum Leptin and the activity of RMCA in hypertensive disorder complicating pregnancy （r = -0.63）. Conclusion： Inhibition of EMCA activity of erythrocyte in hypertensive disorder complicating pregnancy may increase cytoplasmic free calcium, which contributes to the development of hypertensive disorder complicating pregnancy. The negative correlation between the level of serum Leptin and the activity of EMCA, also suggested that serum Leptin and the activity of EMCA may play a role in the development of hypertensive disorder complicating pregnancy.

人晶状体上皮细胞系细胞膜Ca^(2+)-ATPase同工异构体2的表达

目的 检测人晶状体上皮细胞系B 3(HLEB 3)中,细胞膜钙ATP酶(PMCA)的同工异构体之一,PMCA2的表达情况。 方法 细胞培养HLEB 3,当细胞培养达 90%融合时,提取其总mRNA,用PMCA2特异性引物,用反向聚合酶链反应(RT PCR)法检测PMCA2在mRNA水平上的表达。提取细胞膜蛋白,经SDS PAGE电泳以及蛋白免疫印记法(Westernblot),用抗 PMCA2的特异抗体检测其在蛋白质水平上的表达。 结果 RT PCR显示PMCA2特异性引物在HLEB 3细胞扩增出唯一 550bp的片段。蛋白免疫印记法证实PMCA2的表达,相对分子质量约为126 000。 结论 HLEB 3细胞中,在mRNA水平以及蛋白质水平均有PMCA2的表达。并有可能在HLEB 3细胞的钙离子平衡调节中发挥重要作用。

Effects of Calcium on the GABA_A-Coupled CI^-/HCO₃^--ATPase from Plasma Membrane of Rat Brain

The work is a study of the influence of Ca2+ (0.01 - 1 mM) on neuronal CI-, HCO3-, -ATPase complex: an enzyme that is a CI--pump which is functionally and structurally coupled to GABAA-receptors. It is found that influence of Ca2+ on the multifunctional complex starts at concentration of 50·M and at concentration of 0.1 mM, it reduces the “basal” one and increases the CI-, HCO3-, -stimulated Mg2+-ATPase activities. GABA (0.1 - 100μM) activates the “basal” Mg2+-ATPase activity in the ab-sence of calcium. The effect of GABA on the enzyme in the presence of 0.01 ·M Ca2+ does not change. At the same time, 1 mM Ca2+eliminates the GABA effect on the “basal” Mg2+-ATPase activity. Competitive blocker of GABAA-receptors bicuculline (5 - 20 μM) in the absence of Ca2+ ions elimi-nates the stimulation of the “basal” Mg2+-ATPase by anions. When 0.25 mM Ca2+ is added to the in-cubation medium the inhibitory bicuculline effect on the enzyme does not appear. We found that 0.1 mM o-vanadate (protein tyrosine phosphatase blocker) reduces the GABA-activated ATPase activity. At the same time, 0.1 mM genistein (a protein tyrosine kinase blocker) has no effect on enzyme activity. In the presence of Ca2+ (0.25 mM), the effect of o-vanadate on the “basal” and CI-, HCO3-, -ATPase activities does not appear. It is shown for the first time that high concentrations of Ca2+prevent the action of GABAA-ergic ligands on the study ATPase. It is assumed that there is the involvement of protein kinases and protein phosphatases in the modulation of the enzyme activity by calcium. The observed effect of calcium on the ATPase may play an important role in the study of the mechanisms of epileptogenesis and seizure activity.

Plasma membrane calcium pump regulation by metabolic stress

The plasma membrane Ca2+-ATPase(PMCA)is an ATPdriven pump that is critical for the maintenance of low resting[Ca2+]i in all eukaryotic cells.Metabolic stress, either due to inhibition of mitochondrial or glycolytic metabolism,has the capacity to cause ATP depletion and thus inhibit PMCA activity.This has potentially fatal consequences,particularly for non-excitable cells in which the PMCA is the major Ca2+efflux pathway.This is because inhibition of the PMCA inevitably leads to cytosolic Ca2+ overload and the consequent cell death.However,the relationship between metabolic stress,ATP depletion and inhibition of the PMCA is not as simple as one would have originally predicted.There is increasing evidence that metabolic stress can lead to the inhibition of PMCA activity independent of ATP or prior to substantial ATP depletion.In particular,there is evidence that the PMCA has its own glycolytic ATP supply that can fuel the PMCA in the face of impaired mitochondrial function.Moreover, membrane phospholipids,mitochondrial membrane potential,caspase/calpain cleavage and oxidative stress have all been implicated in metabolic stress-induced inhibition of the PMCA.The major focus of this review is to challenge the conventional view of ATP-dependent regulation of the PMCA and bring together some of the alternative or additional mechanisms by which metabolic stress impairs PMCA activity resulting in cytosolic Ca2+ overload and cytotoxicity.

甲基强的松龙对大鼠脊髓损伤后质膜钙ATP同工酶2和神经内分泌蛋白7B2表达的影响

目的:探讨甲基强的松龙(MP)对大鼠脊髓损伤后质膜钙ATP同工酶2(plasm amembrane Ca2+-AT-Paseiso form2)和神经内分泌蛋白7B2(neuroendrocrine protein 7B2)表达的影响。方法:SD大鼠30只。随机分为假手术组、单纯脊髓损伤组(损伤组)、脊髓损伤+大剂量甲基强的松龙治疗组(MP组)。应用改良Allen打击法致T8脊髓损伤。MP组大鼠尾静脉内注射大剂量MP(30mg/kg)。损伤后24h将损伤平面上下0.5cm的脊髓组织切取,进行RT-PCR反应,检测质膜钙ATP同工酶2和神经内分泌蛋白7B2的基因表达情况。结果:在术后24h假手术组质膜钙ATP同工酶2mRNA表达的相对丰度为0.3232±0.0032,损伤组为0.1518±0.069,MP组为0.5721±0.1325,三组间有显著性差异,MP组大于假手术组(P<0.05),假手术组大于损伤组(P<0.01)。假手术组神经内分泌蛋白7B2mRNA表达的相对丰度为1.2289±0.1189,损伤组为0.5843±0.2951,MP组为1.2890±0.2268,MP组和假手术组与损伤组比较差异有显著性(P<0.01),MP组与假手术组比较差异无显著性(P>0.05)。结论:脊髓损伤后,细胞合成质膜钙ATP同工酶2明显降低,邻近损伤处的脊髓组织神经内分泌蛋白7B2的表达降低,大剂量MP能显著促进并逆转质膜钙ATP同工酶2表达的丰度,促进神经内分泌蛋白7B2的表达,发挥细胞保护作用。

Effects of Xianzhen Tablet（仙贞片）on Na^+-K^+-ATPase and Ca^(2+)-Mg^(2+)-ATPase in Erythrocytic Membranes and Viscosity of Whole Blood in Non-Insulin-Dependent Diabetes Patients with Qi-Yin Deficiency, Kidney Deficiency and Blood Stasis

Objective: To assess the effects of Xianzhen tablet (XZT) on Na+-K+ -ATPase and Ca2+ Mg2+-ATPase on erythrocytic membranes, viscosity of whole blood, plasma glucose and clinical manifestations.Methods: Seventy-two cases of non-insulin-dependent diabetes mellitus (NIDDM) patients with deficiency of both Qi and Yin, deficiency of the Kidney and blood stasis were selected, and the effects of treatment on Na+ K + -ATPase, Ca2+-Mg2+ -ATPase, whole blood viscosity, blood sugar and clinical Symptoms were observed.Results: In XZT group (test group), activities of Na+ -K+ -ATPase and Ca2+ -Mg2+ -ATPase rose significantly(P< 0. 01, P< 0. 05) after treatment. Viscosity of whole blood and clinical manifestations also improved obviously. The total effective rate in lowering plasma glucose was 77. 8 % with fasting blood glucose (FBG) and 69.4 % with 2 hours postprandial plasma blood glucose (2°PBG). In the control group, viscosity of whole blood andclinical manifestations had no significant improvement. Its total effective rate in lowering plasma glucose was41. 7% with FBG and 38. 9% with 2°PBG. Conclusions: XZT played a certain role in increasing activities ofNa+ -K + -ATPase and Ca2+-Mg2+ -ATPase, decreasing viscosity of whole blood and plasma glucose and improving clinical manifestations. Therefore, XZT was experimentally manifested as an effective drug in treating NIDDM patients with Qi-Yin deficiency, renal deficiency and blood stasis.

Identification of H^+/Ca^(2+) Antiporter in Barley Root Plasma Membrane

On the basis of two types of calcium transport system detected in the barley root plasma membrane,the mechanisms of the calcium transport have been further studied.Ionophore CCCP has been found to inhibit Mg^(2+) -dependent calcium transport by 20%.In contrast,Mg^(2+) -independent calcium trans- port is insensitive to CCCP.The Mg^(2+) -dependent calcium transport following the collapse of H^+ gradient across the plasma membrane could be driven by the H^+ gradient either set up by ATP or imposed artificially. Any relation between Mg^(2+) -independent calcium transport and H^+ gradient has not been observed.These results indicate that Mg^(2+) -dependent calcium transport is accompanied by the decrease of H^+ gradient,and Mg^(2+) -independent calcium transport has nothing to do with the H^+ gradient.It is therefore suggested that the calcium transport across the barley root plasma membrane is driven by ATPase that is independent of Mg^(2+),and H^+/Ca^(2+) antiporter that is dependent on Mg^(2+).

噪声作业工人钙粘蛋白、质膜Ca^(2+)-ATP酶异构体2基因多态性研究

目的了解噪声性听力损失(NIHL)易感性与钙粘蛋白23(CDH23)、质膜Ca2+-ATP酶异构体2(PM-CA2)基因单核苷酸多态性(SNPs)的关系。方法采用聚合酶链式反应-限制性片段长度多态性法(PCR-RFLP)以及特异性扩增法进行基因型鉴别。结果 Logistic回归分析:CDH23-rs3802711位点的CC基因型与TT基因型的个体相比,NIHL发生风险较高(OR=0.18,95%CI=0.06～0.49,P<0.05);CDH23-Exon7位点GG基因型与AA基因型的个体相比,NIHL发生风险较高(OR=15.87,95%CI=3.91～64.45,P<0.05)。PMCA2-rs2289274位点的AG基因型与GG基因型的个体相比,NIHL发生风险较高(OR=13.60,95%CI=6.09～30.61,P<0.05)。结论 NIHL易感性与CDH23-rs3802711,Exon 7,PMCA2-rs2289274位点有关。

Molecular Cloning and Distribution of a Plasma Membrane Calcium ATPase Homolog from the Pearl Oyster Pinctada fucata

Plasma membrane calcium ATPase （PMCA） plays a critical role in transporting Ca^2＋ out of the cytosol across the plasma membrane which is essential both in keeping intracellular Ca^2＋ homeostasis and in biomineralization. In this paper we cloned and localized a gene encoding PMCA from the pearl oyster Pinctada fucata. This PMCA shares similarity with other published PMCAs within the functional domains. Reverse transcription-polymerase chain reaction analysis shows that it is expressed ubiquitously. Furthermore, in situ hybridization reveals that it is expressed in the inner epithelial cells of the outer fold and in the outer epithelial cells of the middle fold, as well as the edge near the shell, which suggests that PMCA may be involved in calcified layer formation. The identification and characterization of oyster PMCA can help to further understand the structural and functional properties of molluscan PMCA, as well as the mechanism of maintaining Ca^2＋ homeostasis and the mechanism of mineralization in pearl oyster.

质膜钙ATP酶异构体1～3在新生大鼠耳蜗基底膜的表达

目的通过Western blot方法检测质膜钙ATP酶异构体1～3（plasma membrane Ca2＋-ATPase isoforms 1～3,PMCA1～3）在新生大鼠耳蜗基底膜（basilar membrane,BM）的表达,并检测PMCA2在单个新生大鼠耳蜗毛细胞纤毛的表达量。方法 1取出生后2天（P2）和8天（P8）健康SD大鼠各4只,断头后分离出BM,提取总蛋白,分别取20μg,通过Western blot法检测BM的PMCA1～3表达。2取P2和P8大鼠BM总蛋白3μg,通过Western blot方法检测BM的PMCA2的表达。3取4只P8大鼠,分离出BM,提取总蛋白,分别取5、10、20μg总蛋白并取100、400和800ng牛血清白蛋白（BSA）作为对照组,跑完电泳后将胶分为2部分,部分泳道用于SYPRO染胶,其余泳道用于Western blot检测PMCA2的表达。结果 1在20μg的P2和P8大鼠BM总蛋白中,PMCA1仅有微弱的表达（分别为0.126±0.024、0.131±0.012）,PMCA2表达水平较高（分别为4.16±0.528、4.25±0.319）,PMCA3几乎没有表达（均为0）,三者间差异有统计学意义（P〈0.05）。2在3μg的P2和P8大鼠BM总蛋白中,P8大鼠PMCA2的表达水平（4.571±0.336）高于P2大鼠（3.622±0.285）,差异有统计学意义（P〈0.05）。3PMCA2在单个P8大鼠BM的含量约为2.5ng。结论 PMCA1～3在新生大鼠耳蜗BM的表达水平不同,PMCA2表达量最大,这可能是由于耳蜗毛细胞对这几种PMCA亚型有不同的Ca2＋调节需求。

GABA_A-Coupled Cl-/ HCO₃<sup style="margin-left:-10px">-</sup>-ATPase from Plasma Membrane of the Rat Brain: Role of HCO₃<sup style="margin-left:-10px">-</sup>in the Enzyme Activation

This work examines the influence of Cl- (2.5 - 125 mM) and HCO3- (2 - 30 mM) on the Cl-/HCO3- - ATPase complex of the neuronal membrane and this enzyme is a Cl--pump that is coupled to GABAA receptors. The greatest (44%) activating effect on the enzyme is found with HCO3- (20 - 30 mM), while the maximum activity occurs in the presence of a ratio of ~25 mM HCO3- /~5mM Cl-. Blockers of the GABAA receptor, namely bicuculline (10 - 50 μM) and picrotoxin (50 - 100 μM), inhibit this anion activation, whereas the HCO3- -ATPase activity is not sensitive to these ligands. Autoradiographic analysis of the spectrum of the partially purified enzyme phosphorylated with [γ-32P]ATP allowed us to distinguish three major 32P-labeled protein whose molecular weight are about 57, 53, and 48 kDa. In the presence of 5 mM Cl-/25mM HCO3- and 100 μM picrotoxin, the intensity of the phosphorylation of bands significantly decreased, thereby confirming the assumption about coupled of binding sites for anions and GABAA-ergic ligands. It was suggested scheme of Cl--transport through the plasma membrane by utilizing neuronal Cl-/ -HCO3- ATPase in the low (5 mM) Cl- and high (25 mM) HCO3- concentrations. The data demonstrated for the first time that the GABAA-coupled Cl-/ HCO3- -ATPase from rat brain neuronal membranes is maximally activated at a Cl-/HCO3- ratio of 1:5 and it remains stable at high concentrations of substrate and buffer.