Biomedical subjects

A Livne

Publications and source records attributed to A Livne.

At least 37 records · Page 2Linked to original sources

PubMed1990

Cytoplasmic acidification and activation of Na+/H+ exchange during regulatory volume decrease in Ehrlich ascites tumor cells.

Ehrlich ascites tumor cells undergoing regulatory volume decrease (RVD) exhibit cytoplasmic acidification as measured by an intracellular fluorescent pH indicator. The acidification results in an activation of the Na+/H+ exchanger. The intracellular pH 'set point' for the activation is estimated to be around 7.0. The activation of the Na+H+ exchanger leads to an incomplete RVD. In support of this conclusion, amiloride and Na+-free medium, known to limit the Na+/H+ exchange, indeed enhance the RVD response. Intracellular acidification and activation of Na+/H+ exchange may be a general response of cells undergoing RVD.

Amiloride↗

PubMed1990

Palmitic acid-labeled lipids selectively incorporated into platelet cytoskeleton during aggregation.

Previous experiments showed that during the early stages (20-30 seconds) of aggregation induced by adenosine diphosphate (ADP, 2 microM) or thrombin (0.1 U/mL) of rabbit or human platelets prelabeled with [3H]palmitic acid, labeled lipid became associated with the cytoskeleton isolated after lysis with 1% Triton X-100, 5 mM EGTA [ethylene glycol-bis-(beta-aminoethyl ether)]-N,N,N',N'-tetra-acetic acid. The association appeared to be related to the number of sites of contact and was independent of the release of granule contents. We have now investigated the nature of the labeled lipids by thin-layer and column chromatography and found differences between the distribution of the label in intact platelets (both stimulated and unstimulated) and the isolated cytoskeletons. In both species, and with either ADP or thrombin as aggregating agent, 70-85% of the label in both intact platelets and in the cytoskeletons was in phospholipids. The distribution of label among the phospholipids in the cytoskeletons was similar to that in intact platelets except that the percentage of label in phosphatidylcholine was significantly higher in the cytoskeletons of human platelets than in the intact platelets, and the percentage of label in phosphatidylserine/phosphatidylinositol was significantly lower in the cytoskeletons of rabbit platelets and thrombin-aggregated human platelets than in intact platelets. The cytoskeletons contained a lower percentage of label in triacylglycerol, diacylglycerol, and cholesterol ester than the intact platelets. Contrary to a report in the literature, we found no evidence for the incorporation of diacylglycerol and palmitic acid into the cytoskeleton.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Role of inositol-1-phosphatase inhibition in the mechanism of action of lithium.

Li inhibition of noradrenergic adenylate cyclase may be due to inhibition by Li of agonist-induced increases in GTP binding to G-protein. Such inhibition by Li of G-protein function could have effects on phosphatidyl-inositol-mediated second messenger systems as well as on cyclic AMP-mediated systems. However, Sherman, Berridge and others have proposed that Li affects phosphatidylinositol metabolism by inhibiting inositol-1-phosphatase. We recently have been able to measure inositol-1-phosphatase in human red blood cells. Preliminary data on patients treated with Li compared with controls suggests that the enzyme is indeed inhibited in vivo in patients undergoing Li treatment. However, a series of experiments in rats on addition of inositol to Li treatment did not find that inositol could reverse Li effects. Chronic oral high dose inositol does not reverse Li-induced polyuria (measured by polydipsia), Li-induced weight loss or Li-induced depression of exploratory behavior. These results suggest that Li inhibition of inositol-1-phosphatase indeed occurs in vivo. However, the physiological significance of inositol-1-phosphatase inhibition is not yet established.

Animals↗

PubMed1990

Antinuclear autoantibodies in sera of patients with IgA nephropathy.

IgA nephropathy (IgAN), assumed to be a chronic immune complex glomerulonephritis, has been sometimes associated with various autoimmune diseases and autoimmune phenomena including autoantibody production. The current study was aimed at thoroughly investigating the frequency of raised autoantibody titers against five common nuclear autoantigens in a large number of patients with IgAN as well as patients with other primary immune complex glomerulopathies and normal controls. The incidence of autoantibodies (greater than 2 SD less than 3 SD of controls) in the IgAN group ranged between 13% in the case of anticardiolipin antibodies, and 19% in the case of antiribonucleoprotein antibodies, yet was not found to be significantly different from the incidence observed in the other control groups. In none of the subjects a titer above 3 SD of the means of controls was found. Our study clearly points to the fact that IgAN, while being an immune-mediated disease, is not a clear-cut autoimmune condition. The finding of autoantibodies in these patients may be merely incidental.

Antibodies, Antinuclear↗

PubMed1989

Thrombin-induced platelet aggregation is affected by external Na+ independently of the Na+/H+ exchange.

Thrombin affects blood platelets by activation of Na+/H+ exchange and induction of aggregation, but the relationship between these effects is under debate. The present study attempts to clarify whether the activation of the exchanger activity is required for platelet aggregation. In apparent support of such a requirement, thrombin-induced aggregation is higher in Na+ medium than in N-methylglucamine+ medium and is inhibited by sphingosine, an inhibitor of protein kinase C known to regulate the Na+/H+ exchanger. However, the inhibition of aggregation by sphingosine occurs in both Na+-containing and Na+-free media, the aggregation is identical in Na+ and K+-containing media, and is not inhibited by 5-N-(3-aminophenyl)amiloride, at a concentration 10-fold higher than its Ki for platelet Na+/H+ exchange. Furthermore, at low concentration (0.005 U/ml) thrombin induces aggregation but does not activate the exchange. It is concluded that the activation of Na+/H+ exchange is not required for thrombin-induced platelet aggregation and that the apparent augmentation of aggregation by Na+ is due to an inhibitory effect of N-methylglucamine+.

Adult↗

PubMed1989

Inositol-1-phosphatase of human erythrocytes is inhibited by therapeutic lithium concentrations.

Lithium is widely used in psychiatric chemotherapy and is especially effective in the treatment of manic-depressive illness (MDI), but the mechanism for its therapeutic properties and side effects remains to be elucidated. One of the possibilities relates to the inhibitory effect of Li+ on inositol-1-phosphatase (I-1-P'ase) activity. Indeed, the concentration of inositol-1-phosphate (I-1-P) after treatment with Li+ was shown to be increased in various mammalian cells. Yet, no direct study of I-1-P'ase activity in human cells has been reported. Erythrocytes are readily accessible for routine studies and could facilitate the investigation of I-1-P'ase as affected by Li+ in relation to MDI. It is now shown that I-1-P'ase can be measured in lysate of human erythrocytes, using a small blood sample. The enzymatic activity is localized in the soluble fraction. The Km for I-1-P is 0.14 mM. Intriguingly, the Ki for Li+ is 0.86 mM, within the range of therapeutic concentrations in MDI patients.

Bipolar Disorder↗

PubMed1989

Antinuclear and related autoantibodies in sera of healthy subjects with IgA deficiency.

The sera of 49 healthy IgA-deficient (SIgAD) subjects were evaluated for the presence of autoantibodies directed against 10 different nuclear and cytoskeletal antigens, as well as for the presence of the common lupus anti-DNA idiotype (16/6 Id). Twenty-nine sera were from IgG subclass-deficient subjects (4 = IgG2, 25 = IgG3), and 25 from normal healthy subjects, used as controls. The incidence of antinuclear but not anti-cytoskeletal antibodies were found to be significantly greater in the SIgAD group, as compared to the IgG-deficient subjects and the normal controls. Overall, 39% of SIgAD sera demonstrated polyreactivity, namely reactivity against more than one nuclear antigen. The incidence of specific antibody detection ranged from 37% against cardiolipin to 12% against RNP in the IgA-deficient group, albeit not with statistical significance in all cases when compared to the control group. Isotype evaluation of the antinuclear and related antibodies in the SIgAD group showed a greater tendency towards IgG. This increased incidence of autoantibody production in SIgAD may preceed the development of an overt autoimmune disease in the future.

Agammaglobulinemia↗

PubMed1988

Resolution and reconstitution of interplatelet recognition during aggregation.

In previous studies it was shown that fixed platelets bearing covalently-bound fibrinogen participate passively in release-related aggregation, and that thrombospondin is the released compound which specifically and selectively recognizes the affixed fibrinogen. The present study demonstrates that the phenomenon of passive participation is also obtained with fixed platelets bearing covalently-bound thrombospondin. Moreover, a full resolution and reconstitution of interplatelet recognition during aggregation was obtained with two different systems: (a) fixed platelets bearing affixed fibrinogen were caused to aggregate when stirred and supplemented with soluble thrombospondin; (b) fixed platelets bearing fibrinogen and fixed platelets bearing thrombospondin, each uncapable of undergoing aggregation, aggregated when combined and stirred. It is concluded that fibrinogen and thrombospondin play a major role in the molecular mechanism of interplatelet recognition during aggregation.

Blood Platelets↗

PubMed1988

Na+/H+ exchange and aggregation of human platelets activated by ADP: the exchange is not required for aggregation.

Isolated human blood platelets, loaded with the pH-sensitive fluorescence dye 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein show cytoplasmic alkalinization upon stimulation with thrombin but acidification with ADP stimulation. In both cases a Na+/H+ exchange is activated. This can be revealed by the sensitivity of the induced pH changes to amiloride and to 5-N-(3-aminophenyl)amiloride (APA), known inhibitors of the Na+/H+ exchanger, and by a dependence on sodium in the external medium. ADP-induced platelet aggregation is not affected by omission of sodium from the external medium. Furthermore, aggregation is barely inhibited (less than 10%) by amiloride or APA at concentrations up to 50 microM while the Ki values in affecting the Na+/H+ exchange are 5.9 and 1.6 microM for amiloride and APA, respectively. Platelet aggregation is inhibited by amiloride or APA at concentrations higher than 50 microM, but this inhibition is apparently due to a secondary effect of the agents. It is concluded that platelet aggregation induced by ADP is not dependent on activation of Na+/H+ exchange.

Adenosine Diphosphate↗

PubMed1988

A human monoclonal anti-DNA antibody derived from a patient with polymyositis having the common lupus 16/6 idiotype.

A human IgM monoclonal antibody (Pol-1, SA-1) was generated by the human hybridoma technique from the peripheral blood lymphocytes (PBL) of a patient with active polymyositis. The antibody was found to bind to ssDNA, dsDNA, poly(I) and poly(G) and to carry the common lupus anti-DNA antibody idiotype (16/6 Id). Another human IgM monoclonal antibody (Pol-2, SA-2) produced by similar methods from the PBL of the same patient while in remission lacked the ligand-binding capacities of Pol-1 SA-1 and did not have the 16/6 Id. Analyses of 19 sera samples from patients with polymyositis showed no antinuclear antibodies, excluding a 40% prevalence of the 16/6 Id. The serum of the patient whose lymphocytes were employed to generate the hybridoma was negative for anti-DNA activity as well as for the 16/6 Id. This study suggests that the hybridoma technique may enable expression of dormant idiotypic affinities which do not normally appear in sera.

Antibodies, Antinuclear↗

PubMed1988

The Na+/H+ antiport, cytosolic free Ca2+, and essential hypertension: a hypothesis.

We propose that in essential hypertension higher cytosolic free Ca2+ ([Ca2+]i) is associated with hyperactivity of the Na+/H+ antiport and that augmented activity of this transport system explains at least some abnormalities in Na+ metabolism associated with this disease. In low-renin essential hypertension, a higher [Ca2+]i is present not only in vascular smooth muscle cells of resistance vessels but also in juxtaglomerular cells and renal proximal tubular epithelium. A higher [Ca2+]i in juxtaglomerular cells retards renin secretion, whereas in renal proximal tubules it is associated with increased Na+ reabsorption via the Na+/H+ antiport. Thus, hyperactivity of the Na+/H+ antiport in renal tubular epithelium may be the cause of salt (NaCl) sensitivity. Ca2+ antagonists probably exert their antihypertensive effect by reducing [Ca2+]i in both vascular smooth muscle cells and renal tubular epithelium. These agents are, therefore, particularly effective in the treatment of essential hypertension in blacks and older individuals with the low-renin form of the disease, who are known to be salt sensitive.

Biological Transport↗

PubMed1988

Abundance of the Major Chloroplast Polypeptides during Development and Ripening of Tomato Fruits: An Immunological Study.

During maturation and ripening of tomato (Lycopersicon esculentum, cv Tamar) fruits, there are differential changes in the steady state levels of chloroplast proteins. Western blot analysis indicated that with the exception of the core polypeptide of photosystem I (PSI) (subunit I) the whole complex disappears during the transition of chloroplast to chromoplast. The amounts of the core polypeptide of photosystem II (PSII) (43 kilodaltons) and the light harvesting chlorophyll protein complex increase during maturation and decrease thereafter. In contrast, the 33 kilodalton subunit of PSII is found at the highest levels from the early recorded stages and decreases gradually until late stages of ripening. The level of cytochrome f decreases slowly during the maturation and ripening process, whereas the Rieske protein of the same complex disappears at a faster rate. There are also differential changes in the subunits of the chloroplast coupling factor.ATPase complex; alpha and beta subunits increase during maturation, whereas the level of the gamma subunit is already maximal at the earliest recorded stage of development and depleted thereafter. The two subunits of the ribulose-1,5 bisphosphate carboxylase increase in abundance during chloroplast maturation and gradually disappear after the transition from chloroplast to chromoplast. However, there are substantial differences in the rates of increase and disappearance of the large and small subunits of this enzyme. This imbalance is attributed to different regulation of nuclear and chloroplast gene expression. In addition, the steady state levels of chloroplastic superoxide dismutase and phosphoenolpyruvate carboxylase have been followed. Both enzymes reach their maxima at the final stages of ripening. This increase coincides with the climacteric rise of CO(2) release.

Journal Article↗

PubMed1988

Aggregation-related association of lipid with the cytoskeleton of rabbit and human platelets prelabeled with [3H]palmitic acid. Similar effects of adenosine diphosphate- and thrombin-induced aggregation.

To investigate the association of lipid with the cytoskeleton of platelets during aggregation, rabbit and human platelets were isolated and labeled with [3H]palmitic acid; lipid extraction showed approximately 80% in phospholipid. Limited aggregation was induced with ADP or thrombin, and the cytoskeleton was isolated after lysis with 1% Triton X-100, 5 mM EGTA. Cytoskeleton from unactivated platelets had approximately 0.03% of the total label in the platelets, but after aggregation with ADP (2 microM) or thrombin (0.1 U/ml) for 20-30 s, 1.5-8% of the label was with the cytoskeleton. Fibrinogen enhanced aggregation and the association of label with the cytoskeleton; incorporation of label increased exponentially as aggregation proceeded, decreased exponentially during deaggregation, and appeared to be related to the number of sites of contact. Inhibitors that increase cyclic AMP inhibited aggregation and cytoskeletal labeling, but aspirin had no effect. Some experiments were done with DNase I and Ca2+ in the Triton X-100 lysis medium to cause actin depolymerization, under conditions in which the Ca2+-dependent protease activity was inhibited. This greatly reduced the association of label with the cytoskeleton at early time points, but when aggregation had proceeded further, a large proportion of the label was not dissociated by this treatment. These findings, electron microscopy, and the enrichment of the cytoskeleton of aggregated platelets with only some of the membrane proteins that were labeled by the 125I-lactoperoxidase method, indicated that with limited aggregation, the 3H-labeled lipid was mainly associated with the cytoskeleton and not with trapped membrane fragments resulting from incomplete lysis. Since the pattern of cytoskeleton labeling ([3H]palmitate) and the selective association of some membrane proteins with the cytoskeleton/lipid complex was the same with ADP and thrombin, the reactions must be dependent on aggregation and not on events associated with the release of granule contents.

Actin Cytoskeleton↗

PubMed1988

Comparison of the digitalis receptor in erythrocytes from preterm infants and adults.

We compared 86rubidium by erythrocytes of preterm infants and adults as a measurement of their Na+, K+, ATPase enzyme system. In neonates, total uptake (0.92 +/- 0.13 micrograms/10(6) cells) and specific uptake (0.64 +/- 0.076 micrograms/10(6) cells) were significantly higher than in adults (0.52 +/- 0.1 and 0.29 +/- 0.06 micrograms/10(6) cells, respectively; p less than 0.025). The percentage of specific uptake from total uptake was higher in infants (73.3 +/- 2.3%) than in adults (57.9 +/- 4.6%) (p less than 0.005). No differences were found in the affinity constant of 86Rb uptake between infants (4.35 +/- 0.48 ng/ml) and adults (4.85 +/- 0.48 ng/ml). Stratification of infants according to their serum K+ concentrations revealed that levels above 5.4 mEq/liter were associated with a higher specific uptake (0.79 +/- 0.107 micrograms/10(6) cells) than in normokalemic infants (0.54 +/- 0.09 micrograms/10(6) cells) or adults (0.304 +/- 0.061 micrograms/10(6) cells) (p less than 0.05). The difference between hyperkalemic and normokalemic infants persisted after excluding those who received adult packed cells (0.88 +/- 0.1 and 0.6 +/- 0.12 micrograms/10(6) cells, respectively) (p less than 0.05). Infants with serum K+ greater than 5.8 mEq/liter received on average significantly more K+ in previous days (2.46 +/- 0.49 versus 1.13 + 0.34 mEq/kg.day; p less than 0.025). The different K+ level could not be attributed to different creatinine clearance in the two groups.

Adult↗

PubMed1988

Angiotensin II and Na+/H+ exchange in human blood platelets.

Human blood platelets have a high potency for Na+/H+ exchange activity; they also bear receptors for angiotensin II (Ang II). To explore the effect of Ang II on the exchange, we have used a fluorimetric analysis capable of detecting cytoplasmic changes of 0.01 pH units in platelets, together with an Ang II preparation which has been proven to be effective as a vasoconstrictor. Thrombin and adenosine diphosphate (ADP) affected Na+/H+ exchange, but Ang II did not affect Na+/H+ exchange for a wide range of concentrations and experimental conditions. It is concluded that in contrast to its function in vascular smooth muscle cells, Ang II apparently does not play a role in the regulation of Na+/H+ exchange in human blood platelets.

Angiotensin II↗

PubMed1987

Characterization of Na+/H+ exchange in platelets.

Acidification of the cytoplasm of human blood platelets leads to activation of Na+/H+ exchange. As a result, alkalinization occurs that is detectable by an intracellular fluorescent pH indicator. The activity of the exchanger can also be measured by the swelling of platelets suspended in Na-propionate medium using a Coulter Counter: the rapid entry of propionic acid leads to acidification and activation of Na+/H+ exchange with the parallel entry of Na+ and propionic acid leading to osmotic swelling. The Na+/H+ exchanger is sensitive to amiloride and to derivatives that are reported to be more specific inhibitors; it is specific for Na+ and Li+ with no measurable transfer of K+, Rb+ or Cs+; its Km for Na+ is 75 to 90 mM; it displays competitive behavior between Na+ and amiloride; its activity is decreased in cells loaded with Na+ by prolonged ouabain treatment; and it has a high temperature coefficient. These properties are in general similar to those of the exchanger in other cells. It is suggested that the Na+/H+ exchanger plays a role in platelet pH regulation.

Adult↗

PubMed1987

Elevated intracellular Ca2+ affects Lii-Nao countertransport in human red blood cells.

Changes in cytoplasmic Ca2+ concentration and in Lii-Nao countertransport activity have been shown to be associated with essential hypertension. Elevated intracellular free [Ca2+], as well as abnormalities of Ca2+ binding and transport have been reported in cells from different tissues of hypertensive laboratory animals and essential hypertensive patients. Similarly, enhanced rates of Lii-Nao countertransport and the modified pattern of the temperature dependence of this activity in red blood cells from essential hypertensive patients have been previously demonstrated. The aim of the present study was to investigate possible interaction between changes in intracellular free [Ca2+] and the Lii-Nao exchange in human red blood cells. The ionophore ionomycin was used to allow Ca2+ incorporation into the cells in a dose-dependent manner. The elevation of intracellular [Ca2+], in turn, resulted in enhanced Li+ efflux from the cells. At 3 microM, ionomycin selectively and significantly enhanced the Lii-Nao countertransport but not Li+ leakage from the cells. EGTA totally abolished the effect of ionomycin, indicating that the effect is directly related to Ca2+. As low as 0.4 microM Ca2+ caused a statistically significant effect. The maximal effect of Ca2+ on the Lii-Nao countertransport was achieved around the external pH range of 6.8-7.5. In contrast, the leakage of Li+ was significantly enhanced by Ca2+ at a pH of 7.4 and above. Ca2+ did not affect the Km of the Lii-Nao countertransport for Li+. Amiloride, which inhibits Na+/H+ exchange, inhibited only 10% of the Ca2+-enhanced countertransport. It is concluded that Ca2+ may play a role in the regulation of Lii-Nao countertransport in erythrocytes.

Antiporters↗

PubMed1987

Increased platelet Na+-H+ exchange rates in essential hypertension: application of a novel test.

Enhanced sodium-proton exchange may play a role in the pathogenesis of hypertension. Na+-H+ exchange was measured indirectly in platelets as the rate of amiloride-sensitive and sodium-dependent volume gain of cells suspended in sodium-propionate; the cytoplasmic acidification induced by the permeant propionic acid activated the exchanger and the volume changes coupled to Na+ uptake were measured by cell sizing with a Coulter counter and 'Channelyzer'. The test was rapid, simple, and reproducible. 20 normotensives; 8 normotensives with a family history of hypertension; 15 patients with essential hypertension receiving medication; and 7 hypertensives who had not received any antihypertensive drugs were studied. The exchange rate constants of these groups were (mean [SE] in s-1 X 10(-3)) 13.1 (0.6); 15.5 (0.7); 18.4 (0.9); and 25.6 (2.8), respectively. The differences between hypertensives and normotensives were significant. Measurement of sodium-proton exchange in platelets may help to clarify the pathogenesis of hypertension.

Blood Platelets↗