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A Cittadini

Publications and source records attributed to A Cittadini.

At least 127 records · Page 7Linked to original sources
PubMed1983

Intracellular Mg2+ homeostasis of Ehrlich ascites tumor cells.

Treatment of Ehrlich ascites tumor cells with the cation ionophore A23187 results in cellular accumulation of calcium from the extracellular medium only when cellular metabolism is inhibited by uncouplers and iodoacetate. In the metabolically active cells A23187 induces a substantial loss of intracellular magnesium at extracellular Mg2+ concentrations below 1 mM. By contrast, in the inhibited cells A23187 induces a conspicuous loss of magnesium at concentrations of magnesium in the medium ranging from 0.2 to 5 mM. This cellular magnesium loss is accompanied by an increase in intracellular calcium. At 10 mM external Mg2+, A23187 provokes an intracellular magnesium increase in both metabolically active and inhibited cells with a corresponding H+ ejection. Intracellular free Mg2+ in both control and metabolically inhibited cells was estimated through a null-point titration by monitoring changes in extracellular Mg2+ concentration due to the addition of A23187 to cell suspensions with the metallochromic indicator Antipyrylazo III. Free intracellular Mg2+ was 0.4 and 1.2 mM in metabolically active cells and in cells treated with metabolic inhibitors, respectively. Under these conditions the cellular ATP was 30.9 and 2.3 nmol/mg dry wt, respectively. The results lead to the conclusion that in intact Ehrlich ascites tumor cells the level of ATP mainly regulates the intracellular free Mg2+ concentration and, in turn, intracellular free Mg2+ determines the entry of calcium into the cell after A23187 addition.

Adenine Nucleotides↗
PubMed1982

Calcium permeability of Ehrlich ascites tumour cell plasma membrane in vivo.

Passive Ca2+ entry into Ehrlich ascites tumour cells has been investigated. Passive equilibrium of Ca2+ takes place in ascites tumour cells only under conditions of exhaustive energy depletion. The specific Ca2+ ionophore A23187 does not affect Ca2+ entry into ascites tumour cells under active metabolic conditions, but it increases the rate of Ca2+ equilibration in ascites tumour cells in the early stages of energy depletion. The results of the present experiments lead to the conclusion that in ascites tumour cell plasma membrane Ca2+ permeability is not a limiting step in the regulation of intracellular calcium content, while the energy-dependent Ca2+ extrusion is the main mechanism that prevents uncontrolled intracellular Ca2+ increase. The results taken together support the hypothesis that increased Ca2+ influx into the cell, caused by plasma membrane alteration, is responsible for permanently elevated mitotic activity and for deranged metabolic behavior of these neoplastic cells.

Anaerobiosis↗
PubMed1981

Lack of effect of the Ca2+ ionophore A23187 on tumour cells.

The Ca2+ ionophore A23187 increases intracellular calcium content in normal thymic cells, while it is without effect on the corresponding neoplastic cell (Ascites thymoma) and on Ehrlich ascites tumour cells. The A23187-induced total cell calcium increase in normal thymocytes takes place both in control and energy-depleted cells, while it is lacking in neoplastic cells. In addition the ionophore stimulates aerobic glycolysis of normal thymocytes, whereas it is ineffective on neoplastic cells. The study of intracellular calcium exchange properties reveals that in normal cells the ionophore A23187 provokes a 60% increase of the exchangeable pool together with a more significant, 4-fold enlargement of the unexchangeable pool. These effects are lacking in cancer cells. The data give rise to interesting considerations concerning the regulation and compartmentalization of calcium in neoplastic cells. The results will be also discussed in relation to the models that predict altered cell calcium metabolism as a cause of cancer cell high aerobic glycolysis and uncontrolled growth.

Animals↗
PubMed1981

Further observations on calcium and other divalent cations metabolism in intact Ehrlich ascites tumour cells.

The metabolism of calcium has been investigated in the Ehrlich Ascites Tumour Cells (ATC). ATC extrude Ca2+ actively by an energy-dependent mechanism, supported by both respiration and glycolysis. Extrusion takes place even against a very steep concentration gradient (10 mM Ca2+). Cell calcium content is decreased by monovalent cations (Na+,K+ and Li+), which act independently from their metabolic effects. La3+ inhibits ATC Ca2+ extrusion whereas Ruthenium Red slightly decreases cell calcium content. The antibiotic ionophore A 23187 strongly increases ATC Ca2+ level. the metabolism of other divalent cations (Mg2+, Sr2+ and Mn2+) has been studied. Mg2+ does not show appreciable changes in the various metabolic conditions tested, while Mn2+ and Sr2+ behave quite differently from Ca2+, suggesting a different distribution of these cations in ATC. The experimental findings indicate that Ehrlich Ascites Tumour Cells regulate their calcium content by mechanisms related to plasma membranes while the size and activity of mitochondrial compartment is of minor importance.

Animals↗
PubMed1980

Water and ion metabolism in placenta (III). Net movement of water, monovalent and divalent cations in slices from rabbit placenta, at different periods of gestation, incubated under metabolically favorable conditions.

Rabbit placenta slices incubated at 38 degrees C in oxygenated medium, in the presence of endogenous substrates +5 mM glucose, after a period of preincubation of 120 min at 0--1 degrees C, show a net accumulation of potassium and extrusion of water, sodium and calcium. The movement of potassium, sodium and calcium appears to be related to the rate of oxygen consumption of the slices and to be inversely proportional to the age of the tissue. The efficiency of cations movement is also dependent on the nature and composition of the incubation medium. In this respect the potassium concentration of the medium plays a major role. The movement of water, on the other hand, seems to be completely independent from both the rate of respiration and the age of the tissue. The results are discussed in terms of relation between placenta age and senescence, and efficiency of the mechanisms devoted to the cell regulation of water and ions content.

Animals↗
PubMed1979

Calcium transport and contractile activity in dissociated mammalian heart cells.

A homogeneous population of dissociated myocytes can be obtained by enzymic perfusion of adult rabbit hearts. The external membrane of the dissociated cells is freely permeable to electrolytes and is electrochemically shunted. Nevertheless, in the presence of 0.2--0.6 muM Ca2+, the myocytes undergo phasic contractions. Within the range of Ca2+ concentrations eliciting phasic contractions, the dissociated myocytes exhibit Ca2+ uptake activity that is sustained by endogenous ATP in the presence of oxygen and metabolites, or by hexogenous ATP in the presence of oligomycin and antimycin. The uptake is greatly enhanced by oxalate, an effect that is attributed to the activity of sarcoplasmic reticulum. Addition of the calcium ionophore A23187 prevents the occurrence of both Ca2+ accumulation and phasic contractions. In the presence of the ionophore the myocytes remain relaxed at Ca2+ concentrations (less than 1.0 mM) normally sustaining phasic contractile activity, and undergo irreversible contracture at Ca2+ concentrations (greater than 1.0 muM) sufficient to produce direct activation of the myofibrils. It is concluded that Ca2+ transport by sarcoplasmic reticulum is directly related to the occurrence of phasic contractions in dissociated myocytes prepared from rabbit heart. On the other hand, metabolic activity is required for ATP regeneration.

Adenosine Triphosphate↗
PubMed1979

Water and ion metabolism in placenta. II. Water compartments and electrolytes in slices of rabbit placenta, at different periods of gestation, incubated at 0-1 degree C.

The movement and the distribution of water, sodium, potassium, chloride, magnesium and calcium have been studied in slices prepared from rabbit placentae at different periods of gestation, incubated in condition of depressed metabolism (0-1 degree C). In these conditions the tissue takes up water from the external medium up to a maximum of about 2.0 kg/kg d. wt., which represents 30 per cent of the initial H2O content of the fresh tissue. The extracellular compartment swells progressively and proportionally to the age of the placenta. The sodium and chloride content of the tissue increases while that of potassium decreases and their intracellular concentration reaches, after 120 min, that of the external medium. Magnesium does not show appreciable changes and calcium, too, despite its extreme variability, does not seem to undergo significant variations during the cold incubation. The results obtained show that placenta, like most of other mammalian cell systems, possesses specific metabolism-dependent mechanisms responsible for the maintenance of water distribution and ion gradients among the different tissue compartments. The characteristics and the regulation of these mechanisms are discussed in detail.

Animals↗
PubMed1978

Calcium metabolism in intact isolated thymocytes.

Isolated rat thymocytes incubated under proper metabolic conditions extrude Ca2+ previously taken up under metabolically unfavourable conditions. The extrusion can be supported by both respiratory and glycolytic energy but glycolysis seems to be more efficient for this purpose. La3+ (50--200 micron) and the ionophore A 23187 inhibit cell Ca2+ extrusion. Ruthenium Red (1--100 micron) does not influence cell Ca2+ extrusion while it inhibits the in situ mitochondrial cation uptake. All the results are consistent with a cell regulation model of Ca2+ content in which both plasma membrane and mitochondria co-operate, acting in opposite directions, in order to decrease cytosolic Ca2+ concentration. The possibility of Na+-Ca2+ hetero-exchange participation to cell Ca2+ homeostasis regulation is also discussed.

Animals↗
PubMed1978

Properties of the calcium-extruding mechanism of liver cells.

1. The movements of Ca2+ between liver slices and the suspending medium have been followed with a Ca2+-specific electrode and with measurements of the efflux of 45Ca. 2. A net entry of Ca2+ into the tissue occurred during anaerobiosis. Reoxygenation of the medium resulted in a net extrusion of Ca2+ which was reversed by the addition of a respiratory inhibitor (Amytal), an uncoupler of oxidative phosphorylation (pentachlorophenol) or the divalent-cation-specific ionophore, A23187. 3. The net extrusion of Ca2+ was dependent on the presence of Mg2+ in the medium, but was not prevented by ouabain or by incubation in a Na+-free medium. Extrusion was not prevented by cytochalasin B or colchicine. 4. The undirectional efflux of 45Ca required Mg2+ to attain its maximal rate, and the magnitude was not affected by the presence of ouabain or the absence of Na+ from the medium. 5. It is concluded that extrusion of Ca2+ from liver cells is a metabolically dependent transport process that occurs independently of the exchange of Na+ between tissue and medium.

Aerobiosis↗
PubMed1977

Calcium metabolism in Ehrlich Ascites tumour cells.

Ehrlich ascites tumour cells are able, under the proper experimental conditions, to extrude a substantial amount of Ca2+ from the intracellular space. The Ca2+ extrusion mechanism, probably located at the plasma membrane level, appears to be similar to that found in red blood cells. It is energy-dependent and both respiration and glycolysis are able to drive it. The use of some inhibitors and uncouplers, besides showing that this activity is different from that linked to the mitochondrial Ca2+ pump which acts in the opposite direction, proposes some speculations on the energy compartmentation in the Ehrlich ascites tumour cells.

Animals↗
PubMed1977

Water and ion metabolism in placenta. I. water and ion content of rabbit placenta in different periods of gestation.

Total tissue water of rabbit plancenta decreases by 18% between the 9th day and the end of gestation. In the same period intracellular water decreases by 40% and the extracellular compartment swells. Total tissue sodium and chloride content increase by 34% and 27% respectively from the 16th to the 33rd day while potassium decreases by 30%. The intracellular concentration of these ions does not vary greatly during gestation. Moreover the total tissue magnesium content decreases by about 23% at the end of gestation while its intracellular concentration does not show marked changes. Calcium content of rabbit placenta substantially increases during gestation and intracellular calcium shows a fivefold increase from the 16th to the 33rd day of gestation. The results are discussed in terms of relation between water and ion content and placental tissue growth and aging.

Animals↗
PubMed1975

Energy metabolism of isolated rat thymus cells.

The energy metabolism of rat thymus cells has been investigated using preparations of isolated cells obtained by mechanical treatment of whole organs. The addition of glycolytic substrates such as glucose, pyruvate and lactate stimulates the endogenous respiration of these cells by 50%. On the other hand, succinate, glutamate and malate do not produce any effect. Oligomycin (10 mug/ml) inhibits both endogenous and glucose stimulated respiration by about 40%; 2, 4-DNP (50 muM) increases by 100% glucose induced respiration. The results obtained by using mitochondrial and glycolytic inhibitors as well as aminoxyacetic acid (AOA) and following pyridine nucleotides redox changes, support the idea that in thymus cells glucose is able to induce a great enhancement of O2 consumption both by raising the level of endogenous pyruvate and feeding the mitochondrial respiratory chain with cytosolic reducing equivalents, through an active malate-aspartate shuttle. Thymus cells exhibit a high Pasteur effect (74%). Both AOA and 2,4 DNP are able to stimulate aerobic lactate accumulation by 200% and 100% respectively, indicating that either the redox or phosphate potential do influence the rate of aerobic glycolysis in isolated thymus cells. Similar experiments are also reported on other cells with well known biochemical characteristics.

Animals↗